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@node Arithmetic
@chapter Arithmetic

Unless otherwise noted, all of the functions described in this chapter
will work for real and complex scalar or matrix arguments.

@menu
* Utility Functions::           
* Complex Arithmetic::          
* Trigonometry::                
* Sums and Products::           
* Special Functions::           
* Coordinate Transformations::
* Mathematical Constants::      
@end menu

@node Utility Functions
@section Utility Functions

The following functions are available for working with complex numbers.
Each expects a single argument.  They are called @dfn{mapping functions}
because when given a matrix argument, they apply the given function to
each element of the matrix.

@anchor{doc-ceil}
@deftypefn {Mapping Function} {} ceil (@var{x})
Return the smallest integer not less than @var{x}.  If @var{x} is
complex, return @code{ceil (real (@var{x})) + ceil (imag (@var{x})) * I}.
@end deftypefn


@anchor{doc-cplxpair}
@deftypefn {Function File} {} cplxpair (@var{z}, @var{tol}, @var{dim})
Sort the numbers @var{z} into complex conjugate pairs ordered by 
increasing real part.  With identical real parts, order by increasing
imaginary magnitude. Place the negative imaginary complex number
first within each pair. Place all the real numbers after all the 
complex pairs (those with @code{abs (imag (@var{z}) / @var{z}) < 
@var{tol})}, where the default value of @var{tol} is @code{100 * 
@var{eps}}.

By default the complex pairs are sorted along the first non-singleton
dimension of @var{z}. If @var{dim} is specified, then the complex
pairs are sorted along this dimension.

Signal an error if some complex numbers could not be paired. Requires
all complex numbers to be exact conjugates within tol, or signals an 
error. Note that there are no guarantees on the order of the returned
pairs with identical real parts but differing imaginary parts.

@c Using 'smallexample' to make text fit in page when using 'smallbook'
@smallexample
cplxpair (exp(2i*pi*[0:4]'/5)) == exp(2i*pi*[3; 2; 4; 1; 0]/5)
@end smallexample
@end deftypefn


@anchor{doc-del2}
@deftypefn {Function File} {@var{d} =} del2 (@var{m})
@deftypefnx {Function File} {@var{d} =} del2 (@var{m}, @var{h})
@deftypefnx {Function File} {@var{d} =} del2 (@var{m}, @var{dx}, @var{dy}, @dots{})

Calculates the discrete Laplace operator. If @var{m} is a matrix this is
defined as

@iftex
@tex
$d = {1 \over 4} \left( {d^2 \over dx^2} M(x,y) + {d^2 \over dy^2} M(x,y) \right)$
@end tex
@end iftex
@ifnottex
@example
@group
      1    / d^2            d^2         \
D  = --- * | ---  M(x,y) +  ---  M(x,y) | 
      4    \ dx^2           dy^2        /
@end group
@end example
@end ifnottex

The above to continued to N-dimensional arrays calculating the second
derivative over the higher dimensions.

The spacing between evaluation points may be defined by @var{h}, which is a
scalar defining the spacing in all dimensions. Or alternative, the spacing
in each dimension may be defined separately by @var{dx}, @var{dy}, etc. 
Scalar spacing values give equidistant spacing, whereas vector spacing 
values can be used to specify variable spacing. The length of the vectors
must match the respective dimension of @var{m}. The default spacing value
is 1.

You need at least 3 data points for each dimension. Boundary points are
calculated as the linear extrapolation of the interior points.

@seealso{gradient, diff}
@end deftypefn


@anchor{doc-exp}
@deftypefn {Mapping Function} {} exp (@var{x})
Compute the exponential of @var{x}.  To compute the matrix exponential,
see @ref{Linear Algebra}.
@end deftypefn


@anchor{doc-factor}
@deftypefn {Function File} {@var{p} =} factor (@var{q})
@deftypefnx {Function File} {[@var{p}, @var{n}] =} factor (@var{q})

Return prime factorization of @var{q}. That is @code{prod (@var{p})
== @var{q}}. If @code{@var{q} == 1}, returns 1. 

With two output arguments, returns the unique primes @var{p} and
their multiplicities. That is @code{prod (@var{p} .^ @var{n}) ==
@var{q}}.

@end deftypefn


@anchor{doc-factorial}
@deftypefn {Function File} {} factorial (@var{n})
Return the factorial of @var{n}. If @var{n} is scalar, this is
equivalent to @code{prod (1:@var{n})}.  If @var{n} is an array,
the factorial of the elements of the array are returned.
@end deftypefn


@anchor{doc-fix}
@deftypefn {Mapping Function} {} fix (@var{x})
Truncate @var{x} toward zero.  If @var{x} is complex, return
@code{fix (real (@var{x})) + fix (imag (@var{x})) * I}.
@end deftypefn


@anchor{doc-floor}
@deftypefn {Mapping Function} {} floor (@var{x})
Return the largest integer not greater than @var{x}.  If @var{x} is
complex, return @code{floor (real (@var{x})) + floor (imag (@var{x})) * I}.
@end deftypefn


@anchor{doc-fmod}
@deftypefn {Mapping Function} {} fmod (@var{x}, @var{y})
Compute the floating point remainder of dividing @var{x} by @var{y}
using the C library function @code{fmod}.  The result has the same
sign as @var{x}.  If @var{y} is zero, the result implementation-defined.
@end deftypefn


@anchor{doc-gcd}
@deftypefn {Loadable Function} {@var{g} =} gcd (@var{a1}, @dots{})
@deftypefnx {Loadable Function} {[@var{g}, @var{v1}, @dots{}] =} gcd (@var{a1}, @dots{})

If a single argument is given then compute the greatest common divisor of
the elements of this argument. Otherwise if more than one argument is
given all arguments must be the same size or scalar. In this case the
greatest common divisor is calculated for element individually. All
elements must be integers. For example,

@example
@group
gcd ([15, 20])
    @result{}  5
@end group
@end example

@noindent
and

@example
@group
gcd ([15, 9], [20 18])
    @result{}  5  9
@end group
@end example

Optional return arguments @var{v1}, etc, contain integer vectors such
that,

@ifinfo
@example
@var{g} = @var{v1} .* @var{a1} + @var{v2} .* @var{a2} + @dots{}
@end example
@end ifinfo
@iftex
@tex
$g = v_1 a_1 + v_2 a_2 + \cdots$
@end tex
@end iftex

For backward compatibility with previous versions of this function, when
all arguments are scalar, a single return argument @var{v1} containing
all of the values of @var{v1}, @dots{} is acceptable.
@seealso{lcm, min, max, ceil, floor}
@end deftypefn


@anchor{doc-gradient}
@deftypefn {Function File} {@var{x} = } gradient (@var{M})
@deftypefnx {Function File} {[@var{x}, @var{y}, @dots{}] = } gradient (@var{M})
@deftypefnx {Function File} {[@dots{}] = } gradient (@var{M}, @var{s})
@deftypefnx {Function File} {[@dots{}] = } gradient (@var{M}, @var{dx}, @var{dy}, @dots{})

Calculates the gradient. @code{@var{x} = gradient (@var{M})}
calculates the one dimensional gradient if @var{M} is a vector. If
@var{M} is a matrix the gradient is calculated for each row.

@code{[@var{x}, @var{y}] = gradient (@var{M})} calculates the one
dimensional gradient for each direction if @var{M} if @var{M} is a
matrix. Additional return arguments can be use for multi-dimensional
matrices.

Spacing values between two points can be provided by the
@var{dx}, @var{dy} or @var{h} parameters. If @var{h} is supplied it
is assumed to be the spacing in all directions. Otherwise, separate
values of the spacing can be supplied by the @var{dx}, etc variables.
A scalar value specifies an equidistant spacing, while a vector value
can be used to specify a variable spacing. The length must match
their respective dimension of @var{M}.

At boundary points a linear extrapolation is applied. Interior points
are calculated with the first approximation of the numerical gradient

@example
y'(i) = 1/(x(i+1)-x(i-1)) *(y(i-1)-y(i+1)).
@end example

@end deftypefn


@anchor{doc-lcm}
@deftypefn {Mapping Function} {} lcm (@var{x}, @dots{})
Compute the least common multiple of the elements of @var{x}, or
the list of all the arguments.  For example,

@example
lcm (a1, ..., ak)
@end example

@noindent
is the same as

@example
lcm ([a1, ..., ak]).
@end example

All elements must be the same size or scalar.
@seealso{gcd, min, max, ceil, floor}
@end deftypefn


@anchor{doc-log}
@deftypefn {Mapping Function} {} log (@var{x})
Compute the natural logarithm for each element of @var{x}.  To compute the
matrix logarithm, see @ref{Linear Algebra}.
@seealso{log2, log10, logspace, exp}
@end deftypefn


@anchor{doc-log10}
@deftypefn {Mapping Function} {} log10 (@var{x})
Compute the base-10 logarithm for each element of @var{x}.
@seealso{log, log2, logspace, exp}
@end deftypefn


@anchor{doc-log2}
@deftypefn {Mapping Function} {} log2 (@var{x})
@deftypefnx {Mapping Function} {[@var{f}, @var{e}] =} log2 (@var{x})
Compute the base-2 logarithm of @var{x}.  With two outputs, returns
@var{f} and @var{e} such that
@iftex
@tex
 $1/2 <= |f| < 1$ and $x = f \cdot 2^e$.
@end tex
@end iftex
@ifinfo
 1/2 <= abs(f) < 1 and x = f * 2^e.
@end ifinfo
@seealso{log, log10, logspace, exp}
@end deftypefn


@anchor{doc-max}
@deftypefn {Mapping Function} {} max (@var{x}, @var{y}, @var{dim})
@deftypefnx {Mapping Function} {[@var{w}, @var{iw}] =} max (@var{x})
@cindex Utility Functions
For a vector argument, return the maximum value.  For a matrix
argument, return the maximum value from each column, as a row
vector, or over the dimension @var{dim} if defined. For two matrices
(or a matrix and scalar), return the pair-wise maximum.
Thus,

@example
max (max (@var{x}))
@end example

@noindent
returns the largest element of @var{x}, and

@example
@group
max (2:5, pi)
    @result{}  3.1416  3.1416  4.0000  5.0000
@end group
@end example
@noindent
compares each element of the range @code{2:5} with @code{pi}, and
returns a row vector of the maximum values.

For complex arguments, the magnitude of the elements are used for
comparison.

If called with one input and two output arguments,
@code{max} also returns the first index of the
maximum value(s). Thus,

@example
@group
[x, ix] = max ([1, 3, 5, 2, 5])
    @result{}  x = 5
        ix = 3
@end group
@end example
@end deftypefn


@anchor{doc-min}
@deftypefn {Mapping Function} {} min (@var{x}, @var{y}, @var{dim})
@deftypefnx {Mapping Function} {[@var{w}, @var{iw}] =} min (@var{x})
@cindex Utility Functions
For a vector argument, return the minimum value.  For a matrix
argument, return the minimum value from each column, as a row
vector, or over the dimension @var{dim} if defined. For two matrices
(or a matrix and scalar), return the pair-wise minimum.
Thus,

@example
min (min (@var{x}))
@end example

@noindent
returns the smallest element of @var{x}, and

@example
@group
min (2:5, pi)
    @result{}  2.0000  3.0000  3.1416  3.1416
@end group
@end example
@noindent
compares each element of the range @code{2:5} with @code{pi}, and
returns a row vector of the minimum values.

For complex arguments, the magnitude of the elements are used for
comparison.

If called with one input and two output arguments,
@code{min} also returns the first index of the
minimum value(s). Thus,

@example
@group
[x, ix] = min ([1, 3, 0, 2, 5])
    @result{}  x = 0
        ix = 3
@end group
@end example
@end deftypefn


@anchor{doc-mod}
@deftypefn {Mapping Function} {} mod (@var{x}, @var{y})
Compute modulo function, using

@example
x - y .* floor (x ./ y)
@end example

Note that this handles negative numbers correctly:
@code{mod (-1, 3)} is 2, not -1 as @code{rem (-1, 3)} returns.
Also, @code{mod (@var{x}, 0)} returns @var{x}.

An error message is printed if the dimensions of the arguments do not
agree, or if either of the arguments is complex.
@seealso{rem, round}
@end deftypefn


@anchor{doc-nextpow2}
@deftypefn {Function File} {} nextpow2 (@var{x})
If @var{x} is a scalar, returns the first integer @var{n} such that
@iftex
@tex
 $2^n \ge |x|$.
@end tex
@end iftex
@ifinfo
 2^n >= abs (x).
@end ifinfo

If @var{x} is a vector, return @code{nextpow2 (length (@var{x}))}.
@seealso{pow2}
@end deftypefn


@anchor{doc-nthroot}
@deftypefn {Function File} {} nthroot (@var{x}, @var{n})

Compute the nth root of @var{x}, returning real results for real 
components of @var{x}. For example

@example
@group
nthroot (-1, 3)
@result{} -1
(-1) ^ (1 / 3)
@result{} 0.50000 - 0.86603i
@end group
@end example

@end deftypefn


@anchor{doc-pow2}
@deftypefn {Mapping Function} {} pow2 (@var{x})
@deftypefnx {Mapping Function} {} pow2 (@var{f}, @var{e})
With one argument, computes
@iftex
@tex
 $2^x$
@end tex
@end iftex
@ifinfo
 2 .^ x
@end ifinfo
for each element of @var{x}.  With two arguments, returns
@iftex
@tex
 $f \cdot 2^e$.
@end tex
@end iftex
@ifinfo
 f .* (2 .^ e).
@end ifinfo
@seealso{nextpow2}
@end deftypefn


@anchor{doc-primes}
@deftypefn {Function File} {} primes (@var{n})

Return all primes up to @var{n}.  

Note that if you need a specific number of primes, you can use the
fact the distance from one prime to the next is on average
proportional to the logarithm of the prime.  Integrating, you find
that there are about @math{k} primes less than @math{k \log ( 5 k )}.

The algorithm used is called the Sieve of Erastothenes.
@end deftypefn


@anchor{doc-rem}
@deftypefn {Mapping Function} {} rem (@var{x}, @var{y})
Return the remainder of @code{@var{x} / @var{y}}, computed using the
expression

@example
x - y .* fix (x ./ y)
@end example

An error message is printed if the dimensions of the arguments do not
agree, or if either of the arguments is complex.
@seealso{mod, round}
@end deftypefn


@anchor{doc-round}
@deftypefn {Mapping Function} {} round (@var{x})
Return the integer nearest to @var{x}.  If @var{x} is complex, return
@code{round (real (@var{x})) + round (imag (@var{x})) * I}.
@seealso{rem}
@end deftypefn


@anchor{doc-sign}
@deftypefn {Mapping Function} {} sign (@var{x})
Compute the @dfn{signum} function, which is defined as
@iftex
@tex
$$
{\rm sign} (@var{x}) = \cases{1,&$x>0$;\cr 0,&$x=0$;\cr -1,&$x<0$.\cr}
$$
@end tex
@end iftex
@ifinfo

@example
           -1, x < 0;
sign (x) =  0, x = 0;
            1, x > 0.
@end example
@end ifinfo

For complex arguments, @code{sign} returns @code{x ./ abs (@var{x})}.
@end deftypefn


@anchor{doc-sqrt}
@deftypefn {Mapping Function} {} sqrt (@var{x})
Compute the square root of @var{x}.  If @var{x} is negative, a complex
result is returned.  To compute the matrix square root, see
@ref{Linear Algebra}.
@end deftypefn


@node Complex Arithmetic
@section Complex Arithmetic

The following functions are available for working with complex
numbers.  Each expects a single argument.  Given a matrix they work on
an element by element basis.  In the descriptions of the following
functions,
@iftex
@tex
$z$ is the complex number $x + iy$, where $i$ is defined as
$\sqrt{-1}$.
@end tex
@end iftex
@ifinfo
@var{z} is the complex number @var{x} + @var{i}@var{y}, where @var{i} is
defined as @code{sqrt (-1)}.
@end ifinfo

@anchor{doc-abs}
@deftypefn {Mapping Function} {} abs (@var{z})
Compute the magnitude of @var{z}, defined as
@iftex
@tex
$|z| = \sqrt{x^2 + y^2}$.
@end tex
@end iftex
@ifinfo
|@var{z}| = @code{sqrt (x^2 + y^2)}.
@end ifinfo

For example,

@example
@group
abs (3 + 4i)
     @result{} 5
@end group
@end example
@end deftypefn


@anchor{doc-arg}
@deftypefn {Mapping Function} {} arg (@var{z})
@deftypefnx {Mapping Function} {} angle (@var{z})
Compute the argument of @var{z}, defined as
@iftex
@tex
$\theta = \tan^{-1}(y/x)$.
@end tex
@end iftex
@ifinfo
@var{theta} = @code{atan (@var{y}/@var{x})}.
@end ifinfo
@noindent
in radians. 

For example,

@example
@group
arg (3 + 4i)
     @result{} 0.92730
@end group
@end example
@end deftypefn


@anchor{doc-conj}
@deftypefn {Mapping Function} {} conj (@var{z})
Return the complex conjugate of @var{z}, defined as
@iftex
@tex
$\bar{z} = x - iy$.
@end tex
@end iftex
@ifinfo
@code{conj (@var{z})} = @var{x} - @var{i}@var{y}.
@end ifinfo
@seealso{real, imag}
@end deftypefn


@anchor{doc-imag}
@deftypefn {Mapping Function} {} imag (@var{z})
Return the imaginary part of @var{z} as a real number.
@seealso{real, conj}
@end deftypefn


@anchor{doc-real}
@deftypefn {Mapping Function} {} real (@var{z})
Return the real part of @var{z}.
@seealso{imag, conj}
@end deftypefn


@node Trigonometry
@section Trigonometry

Octave provides the following trigonometric functions.  Angles are
specified in radians.  To convert from degrees to radians multiply by
@iftex
@tex
$\pi/180$
@end tex
@end iftex
@ifinfo
@code{pi/180}
@end ifinfo
 (e.g. @code{sin (30 * pi/180)} returns the sine of 30 degrees).

@anchor{doc-sin}
@deftypefn {Mapping Function} {} sin (@var{x})
Compute the sine of each element of @var{x}.
@end deftypefn

@anchor{doc-cos}
@deftypefn {Mapping Function} {} cos (@var{x})
Compute the cosine of each element of @var{x}.
@end deftypefn

@anchor{doc-tan}
@deftypefn {Mapping Function} {} tan (@var{z})
Compute tangent of each element of @var{x}.
@end deftypefn

@anchor{doc-sec}
@deftypefn {Mapping Function} {} sec (@var{x})
Compute the secant of each element of @var{x}.
@end deftypefn

@anchor{doc-csc}
@deftypefn {Mapping Function} {} csc (@var{x})
Compute the cosecant of each element of @var{x}.
@end deftypefn

@anchor{doc-cot}
@deftypefn {Mapping Function} {} cot (@var{x})
Compute the cotangent of each element of @var{x}.
@end deftypefn


@anchor{doc-asin}
@deftypefn {Mapping Function} {} asin (@var{x})
Compute the inverse sine of each element of @var{x}.
@end deftypefn

@anchor{doc-acos}
@deftypefn {Mapping Function} {} acos (@var{x})
Compute the inverse cosine of each element of @var{x}.
@end deftypefn

@anchor{doc-atan}
@deftypefn {Mapping Function} {} atan (@var{x})
Compute the inverse tangent of each element of @var{x}.
@end deftypefn

@anchor{doc-asec}
@deftypefn {Mapping Function} {} asec (@var{x})
Compute the inverse secant of each element of @var{x}.
@end deftypefn

@anchor{doc-acsc}
@deftypefn {Mapping Function} {} acsc (@var{x})
Compute the inverse cosecant of each element of @var{x}.
@end deftypefn

@anchor{doc-acot}
@deftypefn {Mapping Function} {} acot (@var{x})
Compute the inverse cotangent of each element of @var{x}.
@end deftypefn


@anchor{doc-sinh}
@deftypefn {Mapping Function} {} sinh (@var{x})
Compute the hyperbolic sine of each element of @var{x}.
@end deftypefn

@anchor{doc-cosh}
@deftypefn {Mapping Function} {} cosh (@var{x})
Compute the hyperbolic cosine of each element of @var{x}.
@end deftypefn

@anchor{doc-tanh}
@deftypefn {Mapping Function} {} tanh (@var{x})
Compute hyperbolic tangent of each element of @var{x}.
@end deftypefn

@anchor{doc-sech}
@deftypefn {Mapping Function} {} sech (@var{x})
Compute the hyperbolic secant of each element of @var{x}.
@end deftypefn

@anchor{doc-csch}
@deftypefn {Mapping Function} {} csch (@var{x})
Compute the hyperbolic cosecant of each element of @var{x}.
@end deftypefn

@anchor{doc-coth}
@deftypefn {Mapping Function} {} coth (@var{x})
Compute the hyperbolic cotangent of each element of @var{x}.
@end deftypefn


@anchor{doc-asinh}
@deftypefn {Mapping Function} {} asinh (@var{x})
Compute the inverse hyperbolic sine of each element of @var{x}.
@end deftypefn

@anchor{doc-acosh}
@deftypefn {Mapping Function} {} acosh (@var{x})
Compute the inverse hyperbolic cosine of each element of @var{x}.
@end deftypefn

@anchor{doc-atanh}
@deftypefn {Mapping Function} {} atanh (@var{x})
Compute the inverse hyperbolic tangent of each element of @var{x}.
@end deftypefn

@anchor{doc-asech}
@deftypefn {Mapping Function} {} asech (@var{x})
Compute the inverse hyperbolic secant of each element of @var{x}.
@end deftypefn

@anchor{doc-acsch}
@deftypefn {Mapping Function} {} acsch (@var{x})
Compute the inverse hyperbolic cosecant of each element of @var{x}.
@end deftypefn

@anchor{doc-acoth}
@deftypefn {Mapping Function} {} acoth (@var{x})
Compute the inverse hyperbolic cotangent of each element of @var{x}.
@end deftypefn


Each of these functions expects a single argument.  For matrix arguments,
they work on an element by element basis.  For example,

@example
@group
sin ([1, 2; 3, 4])
     @result{}  0.84147   0.90930
         0.14112  -0.75680
@end group
@end example

@anchor{doc-atan2}
@deftypefn {Mapping Function} {} atan2 (@var{y}, @var{x})
Compute atan (@var{y} / @var{x}) for corresponding elements of @var{y}
and @var{x}.  The result is in range -pi to pi.
@end deftypefn


In addition to the trigonometric functions that work with radians,
Octave also provides the following functions which work with degrees.

@anchor{doc-sind}
@deftypefn {Function File} {} sind (@var{x})
Compute the sine of each element of @var{x}.  Returns zero in elements
for which @code{@var{x}/180} is an integer.
@seealso{sin, cosd, tand, acosd, asind, atand}
@end deftypefn

@anchor{doc-cosd}
@deftypefn {Function File} {} cosd (@var{x})
Compute the cosine of an angle in degrees.  Returns zero in elements
for which @code{(@var{x}-90)/180} is an integer.
@seealso{cos, sind, tand, acosd, asind, atand}
@end deftypefn

@anchor{doc-tand}
@deftypefn {Function File} {} tand (@var{x})
Compute the tangent of an angle in degrees.  Returns zero for elements
of for which @code{@var{x}/180} is an integer and @code{Inf} for elements
where @code{(@var{x}-90)/180} is an integer.
@seealso{tan, cosd, sind, acosd, asind, atand}
@end deftypefn

@anchor{doc-secd}
@deftypefn {Function File} {} secd (@var{x})
Compute the secant of an angle in degrees.
@seealso{sec, cscd, sind, cosd}
@end deftypefn

@anchor{doc-cscd}
@deftypefn {Function File} {} cscd (@var{x})
Compute the cosecant of an angle in degrees.
@seealso{csc, secd, sind, cosd}
@end deftypefn

@anchor{doc-cotd}
@deftypefn {Function File} {} cotd (@var{x})
Compute the cotangent of an angle in degrees.
@seealso{cot, tand}
@end deftypefn


@anchor{doc-asind}
@deftypefn {Function File} {} asind (@var{x})
Compute the inverse sine of an angle in degrees.
@seealso{asin, sind, acosd}
@end deftypefn

@anchor{doc-acosd}
@deftypefn {Function File} {} acosd (@var{x})
Compute the inverse cosine of an angle in degrees.
@seealso{acos, cosd, asecd}
@end deftypefn

@anchor{doc-atand}
@deftypefn {Function File} {} atand (@var{x})
Compute the inverse tangent of an angle in degrees.
@seealso{acot, tand}
@end deftypefn

@anchor{doc-asecd}
@deftypefn {Function File} {} asecd (@var{x})
Compute inverse secant in degrees.
@seealso{asec, secd, acscd}
@end deftypefn

@anchor{doc-acscd}
@deftypefn {Function File} {} acscd (@var{x})
Compute the inverse cosecant of an angle in degrees.
@seealso{acsc, cscd, asecd}
@end deftypefn

@anchor{doc-acotd}
@deftypefn {Function File} {} acotd (@var{x})
Compute the inverse cotangent of an angle in degrees.
@seealso{atan, tand}
@end deftypefn


@node Sums and Products
@section Sums and Products

@anchor{doc-sum}
@deftypefn {Built-in Function} {} sum (@var{x}, @var{dim})
@deftypefnx {Built-in Function} {} sum (@dots{}, 'native')
Sum of elements along dimension @var{dim}.  If @var{dim} is
omitted, it defaults to 1 (column-wise sum).

As a special case, if @var{x} is a vector and @var{dim} is omitted,
return the sum of the elements.

If the optional argument 'native' is given, then the sum is performed
in the same type as the original argument, rather than in the default
double type. For example

@example
sum ([true, true])
  @result{} 2
sum ([true, true], 'native')
  @result{} true
@end example
@end deftypefn


@anchor{doc-prod}
@deftypefn {Built-in Function} {} prod (@var{x}, @var{dim})
Product of elements along dimension @var{dim}.  If @var{dim} is
omitted, it defaults to 1 (column-wise products).

As a special case, if @var{x} is a vector and @var{dim} is omitted,
return the product of the elements.
@end deftypefn


@anchor{doc-cumsum}
@deftypefn {Built-in Function} {} cumsum (@var{x}, @var{dim})
Cumulative sum of elements along dimension @var{dim}.  If @var{dim}
is omitted, it defaults to 1 (column-wise cumulative sums).

As a special case, if @var{x} is a vector and @var{dim} is omitted,
return the cumulative sum of the elements as a vector with the
same orientation as @var{x}.
@end deftypefn


@anchor{doc-cumprod}
@deftypefn {Built-in Function} {} cumprod (@var{x}, @var{dim})
Cumulative product of elements along dimension @var{dim}.  If
@var{dim} is omitted, it defaults to 1 (column-wise cumulative
products).

As a special case, if @var{x} is a vector and @var{dim} is omitted,
return the cumulative product of the elements as a vector with the
same orientation as @var{x}.
@end deftypefn


@anchor{doc-sumsq}
@deftypefn {Built-in Function} {} sumsq (@var{x}, @var{dim})
Sum of squares of elements along dimension @var{dim}.  If @var{dim}
is omitted, it defaults to 1 (column-wise sum of squares).

As a special case, if @var{x} is a vector and @var{dim} is omitted,
return the sum of squares of the elements.

This function is conceptually equivalent to computing
@example
sum (x .* conj (x), dim)
@end example
but it uses less memory and avoids calling conj if @var{x} is real.
@end deftypefn


@anchor{doc-accumarray}
@deftypefn {Function File} {} accumarray (@var{subs}, @var{vals}, @var{sz}, @var{fun}, @var{fillval}, @var{issparse})
@deftypefnx {Function File} {} accumarray (@var{csubs}, @var{vals}, @dots{})

Create an array by accumulating the elements of a vector into the
positions defined by their subscripts. The subscripts are defined by
the rows of the matrix @var{subs} and the values by @var{vals}. Each row
of @var{subs} corresponds to one of the values in @var{vals}.

The size of the matrix will be determined by the subscripts themselves.
However, if @var{sz} is defined it determines the matrix size. The length
of @var{sz} must correspond to the number of columns in @var{subs}.

The default action of @code{accumarray} is to sum the elements with the
same subscripts. This behavior can be modified by defining the @var{fun}
function. This should be a function or function handle that accepts a 
column vector and returns a scalar. The result of the function should not
depend on the order of the subscripts.

The elements of the returned array that have no subscripts assoicated with
them are set to zero. Defining @var{fillval} to some other value allows
these values to be defined.

By default @code{accumarray} returns a full matrix. If @var{issparse} is
logically true, then a sparse matrix is returned instead.

An example of the use of @code{accumarray} is:

@example
@group
accumarray ([1,1,1;2,1,2;2,3,2;2,1,2;2,3,2], 101:105)
@result{} ans(:,:,1) = [101, 0, 0; 0, 0, 0]
   ans(:,:,2) = [0, 0, 0; 206, 0, 208]
@end group
@end example
@end deftypefn


@node Special Functions
@section Special Functions

@anchor{doc-besselj}
@deftypefn {Loadable Function} {[@var{j}, @var{ierr}] =} besselj (@var{alpha}, @var{x}, @var{opt})
@deftypefnx {Loadable Function} {[@var{y}, @var{ierr}] =} bessely (@var{alpha}, @var{x}, @var{opt})
@deftypefnx {Loadable Function} {[@var{i}, @var{ierr}] =} besseli (@var{alpha}, @var{x}, @var{opt})
@deftypefnx {Loadable Function} {[@var{k}, @var{ierr}] =} besselk (@var{alpha}, @var{x}, @var{opt})
@deftypefnx {Loadable Function} {[@var{h}, @var{ierr}] =} besselh (@var{alpha}, @var{k}, @var{x}, @var{opt})
Compute Bessel or Hankel functions of various kinds:

@table @code
@item besselj
Bessel functions of the first kind.
@item bessely
Bessel functions of the second kind.
@item besseli
Modified Bessel functions of the first kind.
@item besselk
Modified Bessel functions of the second kind.
@item besselh
Compute Hankel functions of the first (@var{k} = 1) or second (@var{k}
 = 2) kind.
@end table

If the argument @var{opt} is supplied, the result is scaled by the
@code{exp (-I*@var{x})} for @var{k} = 1 or @code{exp (I*@var{x})} for
 @var{k} = 2.

If @var{alpha} is a scalar, the result is the same size as @var{x}.
If @var{x} is a scalar, the result is the same size as @var{alpha}.
If @var{alpha} is a row vector and @var{x} is a column vector, the
result is a matrix with @code{length (@var{x})} rows and
@code{length (@var{alpha})} columns.  Otherwise, @var{alpha} and
@var{x} must conform and the result will be the same size.

The value of @var{alpha} must be real.  The value of @var{x} may be
complex.

If requested, @var{ierr} contains the following status information
and is the same size as the result.

@enumerate 0
@item
Normal return.
@item
Input error, return @code{NaN}.
@item
Overflow, return @code{Inf}.
@item
Loss of significance by argument reduction results in less than
half of machine accuracy.
@item
Complete loss of significance by argument reduction, return @code{NaN}.
@item
Error---no computation, algorithm termination condition not met,
return @code{NaN}.
@end enumerate
@end deftypefn


@anchor{doc-airy}
@deftypefn {Loadable Function} {[@var{a}, @var{ierr}] =} airy (@var{k}, @var{z}, @var{opt})
Compute Airy functions of the first and second kind, and their
derivatives.

@example
 K   Function   Scale factor (if 'opt' is supplied)
---  --------   ---------------------------------------
 0   Ai (Z)     exp ((2/3) * Z * sqrt (Z))
 1   dAi(Z)/dZ  exp ((2/3) * Z * sqrt (Z))
 2   Bi (Z)     exp (-abs (real ((2/3) * Z *sqrt (Z))))
 3   dBi(Z)/dZ  exp (-abs (real ((2/3) * Z *sqrt (Z))))
@end example

The function call @code{airy (@var{z})} is equivalent to
@code{airy (0, @var{z})}.

The result is the same size as @var{z}.

If requested, @var{ierr} contains the following status information and
is the same size as the result.

@enumerate 0
@item
Normal return.
@item
Input error, return @code{NaN}.
@item
Overflow, return @code{Inf}.
@item
Loss of significance by argument reduction results in less than half
 of machine accuracy.
@item
Complete loss of significance by argument reduction, return @code{NaN}.
@item
Error---no computation, algorithm termination condition not met,
return @code{NaN}.
@end enumerate
@end deftypefn


@anchor{doc-beta}
@deftypefn {Mapping Function} {} beta (@var{a}, @var{b})
Return the Beta function,
@iftex
@tex
$$
 B (a, b) = {\Gamma (a) \Gamma (b) \over \Gamma (a + b)}.
$$
@end tex
@end iftex
@ifinfo

@example
beta (a, b) = gamma (a) * gamma (b) / gamma (a + b).
@end example
@end ifinfo
@end deftypefn


@anchor{doc-betainc}
@deftypefn {Mapping Function} {} betainc (@var{x}, @var{a}, @var{b})
Return the incomplete Beta function,
@iftex
@tex
$$
 \beta (x, a, b) = B (a, b)^{-1} \int_0^x t^{(a-z)} (1-t)^{(b-1)} dt.
$$
@end tex
@end iftex
@ifinfo

@smallexample
                                      x
                                     /
betainc (x, a, b) = beta (a, b)^(-1) | t^(a-1) (1-t)^(b-1) dt.
                                     /
                                  t=0
@end smallexample
@end ifinfo

If x has more than one component, both @var{a} and @var{b} must be
scalars.  If @var{x} is a scalar, @var{a} and @var{b} must be of
compatible dimensions.
@end deftypefn


@anchor{doc-betaln}
@deftypefn {Mapping Function} {} betaln (@var{a}, @var{b})
Return the log of the Beta function,
@iftex
@tex
$$
 B (a, b) = \log {\Gamma (a) \Gamma (b) \over \Gamma (a + b)}.
$$
@end tex
@end iftex
@ifinfo

@example
betaln (a, b) = gammaln (a) + gammaln (b) - gammaln (a + b)
@end example
@end ifinfo
@seealso{beta, betai, gammaln}
@end deftypefn


@anchor{doc-bincoeff}
@deftypefn {Mapping Function} {} bincoeff (@var{n}, @var{k})
Return the binomial coefficient of @var{n} and @var{k}, defined as
@iftex
@tex
$$
 {n \choose k} = {n (n-1) (n-2) \cdots (n-k+1) \over k!}
$$
@end tex
@end iftex
@ifinfo

@example
@group
 /   \
 | n |    n (n-1) (n-2) ... (n-k+1)
 |   |  = -------------------------
 | k |               k!
 \   /
@end group
@end example
@end ifinfo

For example,

@example
@group
bincoeff (5, 2)
@result{} 10
@end group
@end example
@end deftypefn


@anchor{doc-erf}
@deftypefn {Mapping Function} {} erf (@var{z})
Computes the error function,
@iftex
@tex
$$
 {\rm erf} (z) = {2 \over \sqrt{\pi}}\int_0^z e^{-t^2} dt
$$
@end tex
@end iftex
@ifinfo

@smallexample
                         z
                        /
erf (z) = (2/sqrt (pi)) | e^(-t^2) dt
                        /
                     t=0
@end smallexample
@end ifinfo
@seealso{erfc, erfinv}
@end deftypefn


@anchor{doc-erfc}
@deftypefn {Mapping Function} {} erfc (@var{z})
Computes the complementary error function,
@iftex
@tex
$1 - {\rm erf} (z)$.
@end tex
@end iftex
@ifinfo
@code{1 - erf (@var{z})}.
@end ifinfo
@seealso{erf, erfinv}
@end deftypefn


@anchor{doc-erfinv}
@deftypefn {Mapping Function} {} erfinv (@var{z})
Computes the inverse of the error function.
@seealso{erf, erfc}
@end deftypefn


@anchor{doc-gamma}
@deftypefn {Mapping Function} {} gamma (@var{z})
Computes the Gamma function,
@iftex
@tex
$$
 \Gamma (z) = \int_0^\infty t^{z-1} e^{-t} dt.
$$
@end tex
@end iftex
@ifinfo

@example
            infinity
            /
gamma (z) = | t^(z-1) exp (-t) dt.
            /
         t=0
@end example
@end ifinfo
@seealso{gammai, lgamma}
@end deftypefn


@anchor{doc-gammainc}
@deftypefn {Mapping Function} {} gammainc (@var{x}, @var{a})
Compute the normalized incomplete gamma function,
@iftex
@tex
$$
 \gamma (x, a) = {\displaystyle\int_0^x e^{-t} t^{a-1} dt \over \Gamma (a)}
$$
@end tex
@end iftex
@ifinfo

@smallexample
                                x
                      1        /
gammainc (x, a) = ---------    | exp (-t) t^(a-1) dt
                  gamma (a)    /
                            t=0
@end smallexample

@end ifinfo
with the limiting value of 1 as @var{x} approaches infinity.
The standard notation is @math{P(a,x)}, e.g. Abramowitz and Stegun (6.5.1).

If @var{a} is scalar, then @code{gammainc (@var{x}, @var{a})} is returned
for each element of @var{x} and vice versa.

If neither @var{x} nor @var{a} is scalar, the sizes of @var{x} and
@var{a} must agree, and @var{gammainc} is applied element-by-element.
@seealso{gamma, lgamma}
@end deftypefn


@anchor{doc-legendre}
@deftypefn {Function File} {@var{L} =} legendre (@var{n}, @var{X})

Legendre Function of degree n and order m
where all values for m = 0..@var{n} are returned.
@var{n} must be a scalar in the range [0..255].
The return value has one dimension more than @var{x}.

@example
The Legendre Function of degree n and order m

@group
 m        m       2  m/2   d^m
P(x) = (-1) * (1-x  )    * ----  P (x)
 n                         dx^m   n
@end group

with:
Legendre polynomial of degree n

@group
          1     d^n   2    n
P (x) = ------ [----(x - 1)  ] 
 n      2^n n!  dx^n
@end group

legendre(3,[-1.0 -0.9 -0.8]) returns the matrix

@group
 x  |   -1.0   |   -0.9   |  -0.8
------------------------------------
m=0 | -1.00000 | -0.47250 | -0.08000
m=1 |  0.00000 | -1.99420 | -1.98000
m=2 |  0.00000 | -2.56500 | -4.32000
m=3 |  0.00000 | -1.24229 | -3.24000 
@end group
@end example
@end deftypefn


@anchor{doc-lgamma}
@deftypefn {Mapping Function} {} lgamma (@var{x})
@deftypefnx {Mapping Function} {} gammaln (@var{x})
Return the natural logarithm of the absolute value of the gamma
function of @var{x}.
@seealso{gamma, gammai}
@end deftypefn


@anchor{doc-cross}
@deftypefn {Function File} {} cross (@var{x}, @var{y}, @var{dim})
Computes the vector cross product of the two 3-dimensional vectors
@var{x} and @var{y}.

@example
@group
cross ([1,1,0], [0,1,1])
@result{} [ 1; -1; 1 ]
@end group
@end example

If @var{x} and @var{y} are matrices, the cross product is applied 
along the first dimension with 3 elements. The optional argument 
@var{dim} is used to force the cross product to be calculated along
the dimension defined by @var{dim}.
@end deftypefn


@anchor{doc-commutation_matrix}
@deftypefn {Function File} {} commutation_matrix (@var{m}, @var{n})
Return the commutation matrix
@iftex
@tex
 $K_{m,n}$
@end tex
@end iftex
@ifinfo
 K(m,n)
@end ifinfo
 which is the unique
@iftex
@tex
 $m n \times m n$
@end tex
@end iftex
@ifinfo
@var{m}*@var{n} by @var{m}*@var{n}
@end ifinfo
 matrix such that
@iftex
@tex
 $K_{m,n} \cdot {\rm vec} (A) = {\rm vec} (A^T)$
@end tex
@end iftex
@ifinfo
@math{K(m,n) * vec(A) = vec(A')}
@end ifinfo
 for all
@iftex
@tex
 $m\times n$
@end tex
@end iftex
@ifinfo
@math{m} by @math{n}
@end ifinfo
 matrices
@iftex
@tex
 $A$.
@end tex
@end iftex
@ifinfo
@math{A}.
@end ifinfo

If only one argument @var{m} is given,
@iftex
@tex
 $K_{m,m}$
@end tex
@end iftex
@ifinfo
@math{K(m,m)}
@end ifinfo
 is returned.

See Magnus and Neudecker (1988), Matrix differential calculus with
applications in statistics and econometrics.
@end deftypefn


@anchor{doc-duplication_matrix}
@deftypefn {Function File} {} duplication_matrix (@var{n})
Return the duplication matrix
@iftex
@tex
 $D_n$
@end tex
@end iftex
@ifinfo
@math{Dn}
@end ifinfo
 which is the unique
@iftex
@tex
 $n^2 \times n(n+1)/2$
@end tex
@end iftex
@ifinfo
@math{n^2} by @math{n*(n+1)/2}
@end ifinfo
 matrix such that
@iftex
@tex
 $D_n * {\rm vech} (A) = {\rm vec} (A)$
@end tex
@end iftex
@ifinfo
@math{Dn vech (A) = vec (A)}
@end ifinfo
 for all symmetric
@iftex
@tex
 $n \times n$
@end tex
@end iftex
@ifinfo
@math{n} by @math{n}
@end ifinfo
 matrices
@iftex
@tex
 $A$.
@end tex
@end iftex
@ifinfo
@math{A}.
@end ifinfo

See Magnus and Neudecker (1988), Matrix differential calculus with
applications in statistics and econometrics.
@end deftypefn


@node Coordinate Transformations
@section Coordinate Transformations

@anchor{doc-cart2pol}
@deftypefn {Function File} {[@var{theta}, @var{r}] =} cart2pol (@var{x}, @var{y})
@deftypefnx {Function File} {[@var{theta}, @var{r}, @var{z}] =} cart2pol (@var{x}, @var{y}, @var{z})
Transform cartesian to polar or cylindrical coordinates.
@var{x}, @var{y} (and @var{z}) must be of same shape.
@var{theta} describes the angle relative to the x - axis.
@var{r} is the distance to the z - axis (0, 0, z).
@seealso{pol2cart, cart2sph, sph2cart}
@end deftypefn


@anchor{doc-pol2cart}
@deftypefn {Function File} {[@var{x}, @var{y}] =} pol2cart (@var{theta}, @var{r})
@deftypefnx {Function File} {[@var{x}, @var{y}, @var{z}] =} pol2cart (@var{theta}, @var{r}, @var{z})
Transform polar or cylindrical to cartesian coordinates.
@var{theta}, @var{r} (and @var{z}) must be of same shape.
@var{theta} describes the angle relative to the x - axis.
@var{r} is the distance to the z - axis (0, 0, z).
@seealso{cart2pol, cart2sph, sph2cart}
@end deftypefn


@anchor{doc-cart2sph}
@deftypefn {Function File} {[@var{theta}, @var{phi}, @var{r}] =} cart2sph (@var{x}, @var{y}, @var{z})
Transform cartesian to spherical coordinates.
@var{x}, @var{y} and @var{z} must be of same shape.
@var{theta} describes the angle relative to the x - axis.
@var{phi} is the angle relative to the xy - plane.
@var{r} is the distance to the origin (0, 0, 0).
@seealso{pol2cart, cart2pol, sph2cart}
@end deftypefn


@anchor{doc-sph2cart}
@deftypefn {Function File} {[@var{x}, @var{y}, @var{z}] =} sph2cart (@var{theta}, @var{phi}, @var{r})
Transform spherical to cartesian coordinates.
@var{x}, @var{y} and @var{z} must be of same shape.
@var{theta} describes the angle relative to the x-axis.
@var{phi} is the angle relative to the xy-plane.
@var{r} is the distance to the origin (0, 0, 0).
@seealso{pol2cart, cart2pol, cart2sph}
@end deftypefn


@node Mathematical Constants
@section Mathematical Constants

@anchor{doc-I}
@deftypefn {Built-in Function} {} I (@var{x})
@deftypefnx {Built-in Function} {} I (@var{n}, @var{m})
@deftypefnx {Built-in Function} {} I (@var{n}, @var{m}, @var{k}, @dots{})
@deftypefnx {Built-in Function} {} I (@dots{}, @var{class})
Return a matrix or N-dimensional array whose elements are all equal
to the pure imaginary unit, defined as
@iftex
@tex
  $\sqrt{-1}$.
@end tex
@end iftex
@ifinfo
  @code{sqrt (-1)}.
@end ifinfo
Since I (also i, J, and j) is a function, you can use the name(s) for
other purposes.
@end deftypefn


@anchor{doc-Inf}
@deftypefn {Built-in Function} {} Inf (@var{x})
@deftypefnx {Built-in Function} {} Inf (@var{n}, @var{m})
@deftypefnx {Built-in Function} {} Inf (@var{n}, @var{m}, @var{k}, @dots{})
@deftypefnx {Built-in Function} {} Inf (@dots{}, @var{class})
Return a matrix or N-dimensional array whose elements are all Infinity.
The arguments are handled the same as the arguments for @code{eye}.
The optional argument @var{class} may be either @samp{"single"} or
@samp{"double"}.  The default is @samp{"double"}.
@end deftypefn


@anchor{doc-NaN}
@deftypefn {Built-in Function} {} NaN (@var{x})
@deftypefnx {Built-in Function} {} NaN (@var{n}, @var{m})
@deftypefnx {Built-in Function} {} NaN (@var{n}, @var{m}, @var{k}, @dots{})
@deftypefnx {Built-in Function} {} NaN (@dots{}, @var{class})
Return a matrix or N-dimensional array whose elements are all NaN
(Not a Number).  The value NaN is the result of an operation like
@iftex
@tex
$0/0$, or $\infty - \infty$,
@end tex
@end iftex
@ifinfo
0/0, or @samp{Inf - Inf},
@end ifinfo
or any operation with a NaN.

Note that NaN always compares not equal to NaN.  This behavior is
specified by the IEEE standard for floating point arithmetic.  To
find NaN values, you must use the @code{isnan} function.

The arguments are handled the same as the arguments for @code{eye}.
The optional argument @var{class} may be either @samp{"single"} or
@samp{"double"}.  The default is @samp{"double"}.
@end deftypefn


@anchor{doc-pi}
@deftypefn {Built-in Function} {} pi (@var{x})
@deftypefnx {Built-in Function} {} pi (@var{n}, @var{m})
@deftypefnx {Built-in Function} {} pi (@var{n}, @var{m}, @var{k}, @dots{})
@deftypefnx {Built-in Function} {} pi (@dots{}, @var{class})
Return a matrix or N-dimensional array whose elements are all equal
to the ratio of the circumference of a circle to its diameter.
Internally, @code{pi} is computed as @samp{4.0 * atan (1.0)}.
@end deftypefn


@anchor{doc-e}
@deftypefn {Built-in Function} {} e (@var{x})
@deftypefnx {Built-in Function} {} e (@var{n}, @var{m})
@deftypefnx {Built-in Function} {} e (@var{n}, @var{m}, @var{k}, @dots{})
@deftypefnx {Built-in Function} {} e (@dots{}, @var{class})
Return a matrix or N-dimensional array whose elements are all equal
to the base of natural logarithms.  The constant
@iftex
@tex
 $e$
@end tex
@end iftex
@ifinfo
 @var{e}
@end ifinfo
 satisfies the equation
@iftex
@tex
 $\log (e) = 1$.
@end tex
@end iftex
@ifinfo
 @code{log} (@var{e}) = 1.
@end ifinfo
@end deftypefn


@anchor{doc-eps}
@deftypefn {Built-in Function} {} eps (@var{x})
@deftypefnx {Built-in Function} {} eps (@var{n}, @var{m})
@deftypefnx {Built-in Function} {} eps (@var{n}, @var{m}, @var{k}, @dots{})
@deftypefnx {Built-in Function} {} eps (@dots{}, @var{class})
Return a matrix or N-dimensional array whose elements are all eps,
the machine precision.  More precisely, @code{eps} is the largest
relative spacing between any two adjacent numbers in the machine's
floating point system.  This number is obviously system-dependent.  On
machines that support 64 bit IEEE floating point arithmetic, @code{eps}
is approximately
@ifinfo
 2.2204e-16.
@end ifinfo
@iftex
@tex
 $2.2204\times10^{-16}$.
@end tex
@end iftex
@end deftypefn


@anchor{doc-realmax}
@deftypefn {Built-in Function} {} realmax (@var{x})
@deftypefnx {Built-in Function} {} realmax (@var{n}, @var{m})
@deftypefnx {Built-in Function} {} realmax (@var{n}, @var{m}, @var{k}, @dots{})
@deftypefnx {Built-in Function} {} realmax (@dots{}, @var{class})
Return a matrix or N-dimensional array whose elements are all equal
to the largest floating point number that is representable.  The actual
value is system-dependent.  On machines that support 64-bit IEEE
floating point arithmetic, @code{realmax} is approximately
@ifinfo
 1.7977e+308
@end ifinfo
@iftex
@tex
 $1.7977\times10^{308}$.
@end tex
@end iftex
@seealso{realmin}
@end deftypefn


@anchor{doc-realmin}
@deftypefn {Built-in Function} {} realmin (@var{x})
@deftypefnx {Built-in Function} {} realmin (@var{n}, @var{m})
@deftypefnx {Built-in Function} {} realmin (@var{n}, @var{m}, @var{k}, @dots{})
@deftypefnx {Built-in Function} {} realmin (@dots{}, @var{class})
Return a matrix or N-dimensional array whose elements are all equal
to the smallest normalized floating point number that is representable.
The actual value is system-dependent.  On machines that support
64-bit IEEE floating point arithmetic, @code{realmin} is approximately
@ifinfo
 2.2251e-308
@end ifinfo
@iftex
@tex
 $2.2251\times10^{-308}$.
@end tex
@end iftex
@seealso{realmax}
@end deftypefn

