.LP
Xprism3 has a built-in function parser that can be used to generate 
3D data points from a function automatically.  Fill in the function, the X 
and Y minimum and maximum points, and the total number of X and Y points. 
All functions are entered in cartesian coordinates.
An example of a 3D function is 3*cos(x)+sin(y).  Note
that when entering a 3D function, the ONLY accepted variables are "x" and "y".
Attempting to use any variables other than "x" and "y" will cause an error 
message.  
.LP
When providing a function to xprism3, one must make sure that the maximum and 
minimum X and Y points (the bounds of the plot), are specified correctly in the
parameters labeled "Minimum", "Maximum" and "Number of Points", 
respectively.  The defaults are -1 to 1 with a total of 30 points. Be sure
that the function is defined over the interval specified.  If the function 
provided is not defined over the given interval, 3 things may occur:  
.IP (1)
The built-in parser will generate an error message 
.IP (2)
Round-off error may cause the parser to compute points that are
NOT EXACTLY at the point where the function is UNDEFINED.  In this case, xprism3
will go ahead and plot the function to the best of its ability, in spite of the
fact that it is undefined over the specified interval.  Results may or may not
be close to the correct graph of the function.
.IP (3)
If there is an error that the signal handlers in Xprism3 cannot handle, the
package will core dump.
.LP
The function "minimun", "maximum", and "number of points" fields are
string fields. Therefore, for any of these fields a constant such as "pi", 
or an expression such as tan(0.9923) can be entered. The only restriction
is that the expression can not be a function of x or y.
.LP
To plot the 3D function, make sure that all parameters are filled out correctly,
and click on the "PLOT FUNCTION" action button.  The function will be evaluated
as indicated and displayed accroding to the current value of the "plot type"
toggle.
.SH
Points to Be Displayed
.IP 
The option, "points to be displayed", allows the user to window on
a specified portion of the data. Along with windowing the user can
subsample the data to be displayed. Note, All data is read in when
the "Plot File" button is clicked with the mouse. The "points to be displayed"
works on the data read in. The window and subsampling parameter may be changed
for each plot on the "Attributes" subform. The "points to be displayed"
option has three items that can be changed. The following explains these
options:
.RS
.IP "Step Size"
This "Step Size" option specifies how the data should be subsampled
between the begin point and the end point. The default value is 1, every
point.
.IP "Begin Point"
The "Begin Point" specifies the begin point of the data to plot. That is
what data point number to begin with. If the "Begin Point" is set to
0, then the "end point" is ignored and all data points are used.
.IP "End Point"
The "End Point" specifies the end point of the data to plot. That is
what data point number to end with. If the "End Point" is set to
0, then the last data point in the file is used as the end point.
.RE
.SH
Plot Type
.IP 
Each plot that is input will be displayed as the plot type that is indicated
by the "plot type" toggle in the "Input File" pane.  Thus, by changing
the plot type before each new plot is displayed, any of the nine plot types
may be displayed simultaneously in the graphics workspace.
