;;; -*-  Mode: Lisp; Package: Maxima; Syntax: Common-Lisp; Base: 10 -*- ;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;     The data in this file contains enhancments.                    ;;;;;
;;;                                                                    ;;;;;
;;;  Copyright (c) 1984,1987 by William Schelter,University of Texas   ;;;;;
;;;     All rights reserved                                            ;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;     (c) Copyright 1981 Massachusetts Institute of Technology         ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(in-package :maxima)

(macsyma-module laplac)

(declare-top (special var $savefactors
		      checkfactors $ratfac $keepfloat *nounl* *nounsflag*
                      errcatch $errormsg))

;;; The properties NOUN and VERB give correct linear display

(defprop $laplace %laplace verb)
(defprop %laplace $laplace noun)

(defprop $ilt %ilt verb)
(defprop %ilt $ilt noun)

(defun exponentiate (pow)
       ;;;COMPUTES %E**Z WHERE Z IS AN ARBITRARY EXPRESSION TAKING SOME OF THE WORK AWAY FROM SIMPEXPT
  (cond ((zerop1 pow) 1)
	((equal pow 1) '$%e)
	(t (power '$%e pow))))

(defun fixuprest (rest)
       ;;;REST IS A PRODUCT WITHOUT THE MTIMES.FIXUPREST PUTS BACK THE MTIMES
  (cond ((null rest) 1)
	((cdr rest) (cons '(mtimes) rest))
	(t (car rest))))

(defun isquadraticp (e x)
  (let ((b (sdiff e x)))
    (cond ((zerop1 b) (list 0 0 e))
	  ((freeof x b) (list 0 b (maxima-substitute 0 x e)))
	  ((setq b (islinear b x))
	   (list (div* (car b) 2) (cdr b) (maxima-substitute 0 x e))))))

;;;INITIALIZES SOME GLOBAL VARIABLES THEN CALLS THE DISPATCHING FUNCTION

(defmfun $laplace (fun var parm)
  (setq fun (mratcheck fun))
  (cond ((or *nounsflag* (member '%laplace *nounl* :test #'eq))
         (setq fun (remlaplace fun))))
  (cond ((and (null (atom fun)) (eq (caar fun) 'mequal))
	 (list '(mequal)
	       (laplace (cadr fun) parm)
	       (laplace (caddr fun) parm)))
	(t (laplace fun parm))))

;;;LAMBDA BINDS SOME SPECIAL VARIABLES TO NIL AND DISPATCHES

(defun remlaplace (e)
  (if (atom e)
      e
      (cons (delete 'laplace (append (car e) nil) :count 1 :test #'eq)
	    (mapcar #'remlaplace (cdr e)))))

(defun laplace (fun parm &optional (dvar nil))
  (let ()
;;; Handles easy cases and calls appropriate function on others.
    (cond ((equal fun 0) 0)
	  ((equal fun 1)
	   (cond ((zerop1 parm) (simplify (list '($delta) 0)))
		 (t (power parm -1))))
	  ((alike1 fun var) (power parm -2))
	  ((or (atom fun) (freeof var fun))
	   (cond ((zerop1 parm) (mul2 fun (simplify (list '($delta) 0))))
		 (t (mul2 fun (power parm -1)))))
	  (t 
           (let ((op (caar fun)))
             (let ((result ; We store the result of laplace for further work.
	       (cond ((eq op 'mplus)
		      (laplus fun parm))
		     ((eq op 'mtimes)
		      (laptimes (cdr fun) parm))
		     ((eq op 'mexpt)
		      (lapexpt fun nil parm))
		     ((eq op '%sin)
		      (lapsin fun nil nil parm))
		     ((eq op '%cos)
		      (lapsin fun nil t parm))
		     ((eq op '%sinh)
		      (lapsinh fun nil nil parm))
		     ((eq op '%cosh)
		      (lapsinh fun nil t parm))
		     ((eq op '%log)
		      (laplog fun parm))
		     ((eq op '%derivative)
		      (lapdiff fun parm))
		     ((eq op '%integrate)
		      (lapint fun parm dvar))
		     ((eq op '%sum)
		      (list '(%sum)
			    (laplace (cadr fun) parm)
			    (caddr fun)
			    (cadddr fun)
			    (car (cddddr fun))))
		     ((eq op '%erf)
		      (laperf fun parm))
		     ((and (eq op '%ilt)(eq (cadddr fun) var))
		      (cond ((eq parm (caddr fun))(cadr fun))
			    (t (subst parm (caddr fun)(cadr fun)))))
                     ((eq op '$delta)
		      (lapdelta fun nil parm))
		     ((setq op ($get op '$laplace))
		      (mcall op fun var parm))
		     (t (lapdefint fun parm)))))
              (when (isinop result '%integrate)
                ;; Laplace has not found a result but returns a definit
                ;; integral. This integral can contain internal integration 
                ;; variables. Replace such a result with the noun form.
                (setq result (list '(%laplace) fun var parm)))
              ;; Check if we have a result, when not call $specint.
              (check-call-to-$specint result fun parm)))))))

;;; Check if laplace has found a result, when not try $specint.

(defun check-call-to-$specint (result fun parm)
  (cond 
    ((or (isinop result '%laplace)
         (isinop result '%limit)   ; Try $specint for incomplete results
         (isinop result '%at))     ; which contain %limit or %at too.
     ;; laplace returns a noun form or a result which contains %limit or %at.
     ;; We pass the function to $specint to look for more results.
     (let (res)
       ;; laplace assumes the parameter s to be positive and does a
       ;; declaration before an integration is done. Therefore we declare
       ;; the parameter of the Laplace transform to be positive before 
       ;; we call $specint too.
       (with-new-context (context)
         (meval `(($assume) ,@(list (list '(mgreaterp) parm 0))))
         (setq res ($specint (mul fun (power '$%e (mul -1 var parm))) var)))
       (if (or (isinop res '%specint)  ; Both symobls are possible, that is
               (isinop res '$specint)) ; not consistent! Check it! 02/2009
           ;; $specint has not found a result.
           result
           ;; $specint has found a result
           res)))
       (t result)))

(defun laplus (fun parm)
  (simplus (cons '(mplus) (mapcar #'(lambda (e) (laplace e parm)) (cdr fun))) 1 t))

(defun laptimes (fun parm)
       ;;;EXPECTS A LIST (PERHAPS EMPTY) OF FUNCTIONS MULTIPLIED TOGETHER WITHOUT THE MTIMES
       ;;;SEES IF IT CAN APPLY THE FIRST AS A TRANSFORMATION ON THE REST OF THE FUNCTIONS
  (cond ((null fun) (list '(mexpt) parm -1.))
	((null (cdr fun)) (laplace (car fun) parm))
	((freeof var (car fun))
	 (simptimes (list '(mtimes)
			  (car fun)
			  (laptimes (cdr fun) parm))
		    1
		    t))
	((eq (car fun) var)
	 (simptimes (list '(mtimes) -1 (sdiff (laptimes (cdr fun) parm) parm))
		    1
		    t))
	(t
	 (let ((op (caaar fun)))
	   (cond ((eq op 'mexpt)
		  (lapexpt (car fun) (cdr fun) parm))
		 ((eq op 'mplus)
		  (laplus ($multthru (fixuprest (cdr fun)) (car fun)) parm))
		 ((eq op '%sin)
		  (lapsin (car fun) (cdr fun) nil parm))
		 ((eq op '%cos)
		  (lapsin (car fun) (cdr fun) t parm))
		 ((eq op '%sinh)
		  (lapsinh (car fun) (cdr fun) nil parm))
		 ((eq op '%cosh)
		  (lapsinh (car fun) (cdr fun) t parm))
		 ((eq op '$delta)
		  (lapdelta (car fun) (cdr fun) parm))
		 (t
		  (lapshift (car fun) (cdr fun) parm)))))))

(defun lapexpt (fun rest parm)
       ;;;HANDLES %E**(A*T+B)*REST(T), %E**(A*T**2+B*T+C),
       ;;; 1/SQRT(A*T+B), OR T**K*REST(T)
  (prog (ab base-of-fun power result)
     (setq base-of-fun (cadr fun) power (caddr fun))
     (cond
       ((and
	 (freeof var base-of-fun)
	 (setq
	  ab
	  (isquadraticp
	   (cond ((eq base-of-fun '$%e) power)
		 (t (simptimes (list '(mtimes)
				     power
				     (list '(%log)
					   base-of-fun))
			       1
			       nil)))
	   var)))
	(cond ((equal (car ab) 0) (go %e-case-lin))
	      ((null rest) (go %e-case-quad))
	      (t (go noluck))))
       ((and (eq base-of-fun var) (freeof var power))
	(go var-case))
       ((and (alike1 '((rat) -1 2) power) (null rest)
	     (setq ab (islinear base-of-fun var)))
	(setq result (div* (cdr ab) (car ab)))
	(return (simptimes
		 (list '(mtimes)
		       (list '(mexpt)
			     (div* '$%pi
				   (list '(mtimes)
					 (car ab)
					 parm))
			     '((rat) 1 2))
		       (exponentiate (list '(mtimes) result parm))
		       (list '(mplus)
			     1
			     (list '(mtimes)
				   -1
				   (list '(%erf)
					 (list '(mexpt)
					       (list '(mtimes)
						     result
						     parm)
					       '((rat) 1 2)))
				   ))) 1 nil)))
       (t (go noluck)))
     %e-case-lin
     (setq result
      (cond
	(rest (sratsimp ($at (laptimes rest parm)
			     (list '(mequal)
				   parm
				   (list '(mplus)
					 parm
					 (afixsign (cadr ab)
						   nil))))))
	(t (list '(mexpt)
		 (list '(mplus)
		       parm
		       (afixsign (cadr ab) nil))
		 -1))))
     (return (simptimes (list '(mtimes)
			      (exponentiate (caddr ab))
			      result)
			1
			nil))
     %e-case-quad
     (setq result (afixsign (car ab) nil))
     (setq
      result
      (list
       '(mtimes)
       (div* (list '(mexpt)
		   (div* '$%pi result)
		   '((rat) 1 2))
	     2)
       (exponentiate (div* (list '(mexpt) parm 2)
			   (list '(mtimes) 4 result)))
       (list '(mplus)
	     1
	     (list '(mtimes)
		   -1
		   (list '(%erf)
			 (div* parm
			       (list '(mtimes)
				     2
				     (list '(mexpt)
					   result
					   '((rat) 1 2)))))
		   ))))
     (and (null (equal (cadr ab) 0))
	  (setq result
		(maxima-substitute (list '(mplus)
					 parm
					 (list '(mtimes)
					       -1
					       (cadr ab)))
				   parm
				   result)))
     (return (simptimes  (list '(mtimes)
			       (exponentiate (caddr ab))
			       result) 1 nil))
     var-case
     (cond ((or (null rest) (freeof var (fixuprest rest)))
	    (go var-easy-case)))
     (cond ((posint power)
	    (return (afixsign (apply '$diff
				     (list (laptimes rest parm)
					   parm
					   power))
			      (even power))))
	   ((negint power)
	    (return (mydefint (hackit power rest parm)
			      (createname parm (- power))
			      parm parm)))
	   (t (go noluck)))
     var-easy-case
     (setq power
	   (simplus (list '(mplus) 1 power) 1 t))
     (or (eq (asksign power) '$positive) (go noluck))
     (setq result (list (list '(%gamma) power)
			(list '(mexpt)
			      parm
			      (afixsign power nil))))
     (and rest (setq result (nconc result rest)))
     (return (simptimes (cons '(mtimes) result) 1 nil))
     noluck
     (return
       (cond
	 ((and (posint power)
	       (member (caar base-of-fun)
		     '(mplus %sin %cos %sinh %cosh) :test #'eq))
	  (laptimes (cons base-of-fun
			  (cons (cond ((= power 2) base-of-fun)
				      (t (list '(mexpt)
					       base-of-fun
					       (1- power))))
				rest)) parm))
	 (t (lapshift fun rest parm))))))

;;;INTEGRAL FROM A TO INFINITY OF F(X)
(defun mydefint (f x a parm)
  (let ((tryint (and (not ($unknown f))
                     ;; We don't want any errors thrown by $defint to propagate,
                     ;; so we set errset, errcatch, $errormsg and *mdebug*.  If
                     ;; $defint throws a error, then no error message is printed
                     ;; and errset simply returns nil below.
                     (with-new-context (context)
                       (meval `(($assume) ,@(list (list '(mgreaterp) parm 0))))
                       (meval `(($assume) ,@(list (list '(mgreaterp) x 0))))
                       (meval `(($assume) ,@(list (list '(mgreaterp) a 0))))
                       (let ((errset nil)
                             (errcatch t)
                             ($errormsg nil)
                             (*mdebug* nil))
                         (errset ($defint f x a '$inf)))))))
    (if tryint
	(car tryint)
	(list '(%integrate) f x a '$inf))))

 ;;;CREATES UNIQUE NAMES FOR VARIABLE OF INTEGRATION
(defun createname (head tail)
  (intern (format nil "~S~S" head tail)))

;;;REDUCES LAPLACE(F(T)/T**N,T,S) CASE TO LAPLACE(F(T)/T**(N-1),T,S) CASE
(defun hackit (exponent rest parm)
  (cond ((equal exponent -1)
	 (let ((parm (createname parm 1)))
	   (laptimes rest parm)))
	(t (mydefint (hackit (1+ exponent) rest parm)
		     (createname parm (- -1 exponent))
		     (createname parm (- exponent)) parm))))

(defun afixsign (funct signswitch)
       ;;;MULTIPLIES FUNCT BY -1 IF SIGNSWITCH IS NIL
  (cond (signswitch funct)
	(t (simptimes (list '(mtimes) -1 funct) 1 t))))

(defun lapshift (fun rest parm)
  (cond ((atom fun) (merror "LAPSHIFT: expected a cons, not ~M" fun))
	((or (member 'laplace (car fun) :test #'eq) (null rest))
	 (lapdefint (cond (rest (simptimes (cons '(mtimes)
						 (cons fun rest)) 1 t))
			  (t fun)) parm))
	(t (laptimes (append rest
			     (ncons (cons (append (car fun)
						  '(laplace))
					  (cdr fun)))) parm))))

;;;COMPUTES %E**(W*B*%I)*F(S-W*A*%I) WHERE W=-1 IF SIGN IS T ELSE W=1
(defun mostpart (f parm sign a b)
  (let ((substinfun ($at f
			 (list '(mequal)
			       parm
			       (list '(mplus) parm (afixsign (list '(mtimes) a '$%i) sign))))))
    (if (zerop1 b)
	substinfun
	(list '(mtimes)
	      (exponentiate (afixsign (list '(mtimes) b '$%i) (null sign)))
	      substinfun))))

 ;;;IF WHICHSIGN IS NIL THEN SIN TRANSFORM ELSE COS TRANSFORM
(defun compose (fun parm whichsign a b)
  (let ((result (list '((rat) 1 2)
		      (list '(mplus)
			    (mostpart fun parm t a b)
			    (afixsign (mostpart fun parm nil a b)
				      whichsign)))))
    (sratsimp (simptimes (cons '(mtimes)
			       (if whichsign
				   result
				   (cons '$%i result)))
			 1 nil))))

 ;;;FUN IS OF THE FORM SIN(A*T+B)*REST(T) OR COS
(defun lapsin (fun rest trigswitch parm)
  (let ((ab (islinear (cadr fun) var)))
    (cond (ab
	   (cond (rest
		  (compose (laptimes rest parm)
			   parm
			   trigswitch
			   (car ab)
			   (cdr ab)))
		 (t
		  (simptimes
		   (list '(mtimes)
		    (cond ((zerop1 (cdr ab))
			   (if trigswitch parm (car ab)))
			  (t
			   (cond (trigswitch
				  (list '(mplus)
					(list '(mtimes)
					      parm
					      (list '(%cos) (cdr ab)))
					(list '(mtimes)
					      -1
					      (car ab)
					      (list '(%sin) (cdr ab)))))
				 (t
				  (list '(mplus)
					(list '(mtimes)
					      parm
					      (list '(%sin) (cdr ab)))
					(list '(mtimes)
					      (car ab)
					      (list '(%cos) (cdr ab))))))))
		    (list '(mexpt)
			  (list '(mplus)
				(list '(mexpt) parm 2)
				(list '(mexpt) (car ab) 2))
			  -1))
		   1 nil))))
	  (t
	   (lapshift fun rest parm)))))

 ;;;FUN IS OF THE FORM SINH(A*T+B)*REST(T) OR IS COSH
(defun lapsinh (fun rest switch parm)
  (cond ((islinear (cadr fun) var)
	 (sratsimp
	  (laplus
	   (simplus
	    (list '(mplus)
		  (nconc (list '(mtimes)
			       (list '(mexpt)
				     '$%e
				     (cadr fun))
			       '((rat) 1 2))
			 rest)
		  (afixsign (nconc (list '(mtimes)
					 (list '(mexpt)
					       '$%e
					       (afixsign (cadr fun)
							 nil))
					 '((rat) 1 2))
				   rest)
			    switch))
	    1
	    nil) parm)))
	(t (lapshift fun rest parm))))

 ;;;FUN IS OF THE FORM LOG(A*T)
(defun laplog (fun parm)
  (let ((ab (islinear (cadr fun) var)))
    (cond ((and ab (zerop1 (cdr ab)))
	   (simptimes (list '(mtimes)
			    (list '(mplus)
				  (subfunmake '$psi '(0) (ncons 1))
				  (list '(%log) (car ab))
				  (list '(mtimes) -1 (list '(%log) parm)))
			    (list '(mexpt) parm -1))
		      1 nil))
	  (t
	   (lapdefint fun parm)))))

(defun raiseup (fbase exponent)
  (if (equal exponent 1)
      fbase
      (list '(mexpt) fbase exponent)))

;;TAKES TRANSFORM OF DELTA(A*T+B)*F(T)
(defun lapdelta (fun rest parm)
  (let ((ab (islinear (cadr fun) var))
	(sign nil)
	(recipa nil))
    (cond (ab
	   (setq recipa (power (car ab) -1) ab (div (cdr ab) (car ab)))
	   (setq sign (asksign ab) recipa (simplifya (list '(mabs) recipa) nil))
	   (simplifya (cond ((eq sign '$positive)
			     0)
			    ((eq sign '$zero)
			     (list '(mtimes)
				   (maxima-substitute 0 var (fixuprest rest))
				   recipa))
			    (t
			     (list '(mtimes)
				   (maxima-substitute (neg ab) var (fixuprest rest))
				   (list '(mexpt) '$%e (cons '(mtimes) (cons parm (ncons ab))))
				   recipa)))
		      nil))
	  (t
	   (lapshift fun rest parm)))))

(defun laperf (fun parm)
  (let ((ab (islinear (cadr fun) var)))
    (cond ((and ab (equal (cdr ab) 0))
	   (simptimes (list '(mtimes)
			    (div* (exponentiate (div* (list '(mexpt) parm 2)
						      (list '(mtimes)
							    4
							    (list '(mexpt) (car ab) 2))))
				  parm)
			    (list '(mplus)
				  1
				  (list '(mtimes)
					-1
					(list '(%erf) (div* parm (list '(mtimes) 2 (car ab)))))))
		      1
		      nil))
	  (t
	   (lapdefint fun parm)))))

(defun lapdefint (fun parm)
  (prog (tryint mult)
     (and ($unknown fun)(go skip))
     (setq mult (simptimes (list '(mtimes) (exponentiate
					    (list '(mtimes) -1 var parm)) fun) 1 nil))
     (with-new-context (context)
       (meval `(($assume) ,@(list (list '(mgreaterp) parm 0))))
       (setq tryint
             ;; We don't want any errors thrown by $defint to propagate,
             ;; so we set errset, errcatch, $errormsg and *mdebug*.  If
             ;; $defint throws a error, then no error message is printed
             ;; and errset simply returns nil below.
             (let ((errset nil)
                   (errcatch t)
                   ($errormsg nil)
                   (*mdebug* nil))
               (errset ($defint mult var 0 '$inf)))))
     (and tryint (not (eq (and (listp (car tryint))
			       (caaar tryint))
			  '%integrate))
	  (return (car tryint)))
     skip (return (list '(%laplace) fun var parm))))


(defun lapdiff (fun parm)
;;;FUN IS OF THE FORM DIFF(F(T),T,N) WHERE N IS A POSITIVE INTEGER
  (prog (difflist degree frontend resultlist newdlist order arg2)
     (setq newdlist (setq difflist (copy-tree (cddr fun))))
     (setq arg2 (list '(mequal) var 0))
     a    (cond ((null difflist)
		 (return (cons '(%derivative)
			       (cons (list '(%laplace)
					   (cadr fun)
					   var
					   parm)
				     newdlist))))
		((eq (car difflist) var)
		 (setq degree (cadr difflist)
		       difflist (cddr difflist))
		 (go out)))
     (setq difflist (cdr (setq frontend (cdr difflist))))
     (go a)
     out  (cond ((null (posint degree))
		 (return (list '(%laplace) fun var parm))))
     (cond (frontend (rplacd frontend difflist))
	   (t (setq newdlist difflist)))
     (cond (newdlist (setq fun (cons '(%derivative)
				     (cons (cadr fun)
					   newdlist))))
	   (t (setq fun (cadr fun))))
     (setq order 0)
     loop (decf degree)
     (setq resultlist
	   (cons (list '(mtimes)
		       (raiseup parm degree)
		       ($at ($diff fun var order) arg2))
		 resultlist))
     (incf order)
     (and (> degree 0) (go loop))
     (setq resultlist (cond ((cdr resultlist)
			     (cons '(mplus)
				   resultlist))
			    (t (car resultlist))))
     (return (simplus (list '(mplus)
			    (list '(mtimes)
				  (raiseup parm order)
				  (laplace fun parm))
			    (list '(mtimes)
				  -1
				  resultlist))
		      1 nil))))

 ;;;FUN IS OF THE FORM INTEGRATE(F(X)*G(T)*H(T-X),X,0,T)
(defun lapint (fun parm dvar)
  (prog (newfun parm-list f var-list var-parm-list)
     (and dvar (go convolution))
     (setq dvar (cadr (setq newfun (cdr fun))))
     (and (cddr newfun)
	  (zerop1 (caddr newfun))
	  (eq (cadddr newfun) var)
	  (go convolutiontest))
     notcon
     (setq newfun (cdr fun))
     (cond ((cddr newfun)
	    (cond ((and (freeof var (caddr newfun))
			(freeof var (cadddr newfun)))
		   (return (list '(%integrate)
				 (laplace (car newfun) parm dvar)
				 dvar
				 (caddr newfun)
				 (cadddr newfun))))
		  (t (go giveup))))
	   (t (return (list '(%integrate)
			    (laplace (car newfun) parm dvar)
			    dvar))))
     giveup
     (return (list '(%laplace) fun var parm))
     convolutiontest
     (setq newfun ($factor (car newfun)))
     (cond ((eq (caar newfun) 'mtimes)
	    (setq f (cadr newfun) newfun (cddr newfun)))
	   (t (setq f newfun newfun nil)))
     gothrulist
     (cond ((freeof dvar f)
	    (setq parm-list (cons f parm-list)))
	   ((freeof var f) (setq var-list (cons f var-list)))
	   ((freeof dvar
		    (sratsimp (maxima-substitute (list '(mplus)
						       var
						       dvar)
						 var
						 f)))
	    (setq var-parm-list (cons f var-parm-list)))
	   (t (go notcon)))
     (cond (newfun (setq f (car newfun) newfun (cdr newfun))
		   (go gothrulist)))
     (and
      parm-list
      (return
	(laplace
	 (cons
	  '(mtimes)
	  (nconc parm-list
		 (ncons (list '(%integrate)
			      (cons '(mtimes)
				    (append var-list
					    var-parm-list))
			      dvar
			      0
			      var)))) parm dvar)))
     convolution
     (return
       (simptimes
	(list
	 '(mtimes)
	 (laplace ($expand (maxima-substitute var
					      dvar
					      (fixuprest var-list))) parm dvar)
	 (laplace
	  ($expand (maxima-substitute 0 dvar (fixuprest var-parm-list))) parm dvar))
	1
	t))))

(declare-top (special varlist ratform ils ilt))

(defmfun $ilt (exp ils ilt)
 ;;;EXP IS F(S)/G(S) WHERE F AND G ARE POLYNOMIALS IN S AND DEGR(F) < DEGR(G)
  (let (varlist ($savefactors t) checkfactors $ratfac $keepfloat)
		;;; MAKES ILS THE MAIN VARIABLE
    (setq varlist (list ils))
    (newvar exp)
    (orderpointer varlist)
    (setq var (caadr (ratrep* ils)))
    (cond ((and (null (atom exp))
		(eq (caar exp) 'mequal))
	   (list '(mequal)
		 ($ilt (cadr exp) ils ilt)
		 ($ilt (caddr exp) ils ilt)))
	  ((zerop1 exp) 0)
	  ((freeof ils exp)
	   (list '(%ilt) exp ils ilt))
	  (t (ilt0 exp)))))

(defun maxima-rationalp (le v)
  (cond ((null le))
	((and (null (atom (car le))) (null (freeof v (car le))))
	 nil)
	(t (maxima-rationalp (cdr le) v))))

 ;;;THIS FUNCTION DOES THE PARTIAL FRACTION DECOMPOSITION
(defun ilt0 (exp)
  (prog (wholepart frpart num denom y content real factor
	 apart bpart parnumer ratarg ratform)
     (and (mplusp exp)
	  (return (simplus  (cons '(mplus)
				  (mapcar #'(lambda (f) ($ilt f ils ilt)) (cdr exp))) 1 t)))
     (and (null (atom exp))
	  (eq (caar exp) '%laplace)
	  (eq (cadddr exp) ils)
	  (return (cond ((eq (caddr exp) ilt) (cadr exp))
			(t (subst ilt
				  (caddr exp)
				  (cadr exp))))))
     (setq ratarg (ratrep* exp))
     (or (maxima-rationalp varlist ils)
	 (return (list '(%ilt) exp ils ilt)))
     (setq ratform (car ratarg))
     (setq denom (ratdenominator (cdr ratarg)))
     (setq frpart (pdivide (ratnumerator (cdr ratarg)) denom))
     (setq wholepart (car frpart))
     (setq frpart (ratqu (cadr frpart) denom))
     (cond ((not (zerop1 (car wholepart)))
	    (return (list '(%ilt) exp ils ilt)))
	   ((zerop1 (car frpart)) (return 0)))
     (setq num (car frpart) denom (cdr frpart))
     (setq y (oldcontent denom))
     (setq content (car y))
     (setq real (cadr y))
     (setq factor (pfactor real))
     loop (cond ((null (cddr factor))
		 (setq apart real
		       bpart 1
		       y '((0 . 1) 1 . 1))
		 (go skip)))
     (setq apart (pexpt (car factor) (cadr factor)))
     (setq bpart (car (ratqu real apart)))
     (setq y (bprog apart bpart))
     skip (setq frpart
		(cdr (ratdivide (ratti (ratnumerator num)
				       (cdr y)
				       t)
				(ratti (ratdenominator num)
				       (ratti content apart t)
				       t))))
     (setq
      parnumer
      (cons (ilt1 (ratqu (ratnumerator frpart)
			 (ratti (ratdenominator frpart)
				(ratti (ratdenominator num)
				       content
				       t)
				t))
		  (car factor)
		  (cadr factor))
	    parnumer))
     (setq factor (cddr factor))
     (cond ((null factor)
	    (return (simplus (cons '(mplus) parnumer) 1 t))))
     (setq num (cdr (ratdivide (ratti num (car y) t)
			       (ratti content bpart t))))
     (setq real bpart)
     (go loop)))

(declare-top (special q z))

(defun ilt1 (p q k)
  (let (z)
    (cond ((onep1 k) (ilt3 p ))
	  (t (setq z (bprog q (pderivative q var)))
	     (ilt2 p k)))))


 ;;;INVERTS P(S)/Q(S)**K WHERE Q(S)  IS IRREDUCIBLE
 ;;;DOESN'T CALL ILT3 IF Q(S) IS LINEAR
(defun ilt2 (p k)
  (prog (y a b)
     (and (onep1 k) (return (ilt3 p)))
     (decf k)
     (setq a (ratti p (car z) t))
     (setq b (ratti p (cdr z) t))
     (setq y (pexpt q k))
     (cond
       ((or (null (equal (pdegree q var) 1))
	    (> (pdegree (car p) var) 0))
	(return
	  (simplus
	   (list
	    '(mplus)
	    (ilt2
	     (cdr (ratdivide (ratplus a (ratqu (ratderivative b var) k)) y))
	     k)
	    ($multthru (simptimes (list '(mtimes)
					ilt
					(power k -1)
					(ilt2 (cdr (ratdivide b y)) k))
				  1
				  t)))
	   1
	   t))))
     (setq a (disrep (polcoef q 1))
	   b (disrep (polcoef q 0)))
     (return
       (simptimes (list '(mtimes)
			(disrep p)
			(raiseup ilt k)
			(simpexpt (list '(mexpt)
					'$%e
					(list '(mtimes)
					      -1
					      ilt
					      b
					      (list '(mexpt) a -1)))
				  1
				  nil)
			(list '(mexpt)
			      a
			      (- -1 k))
			(list '(mexpt)
			      (factorial k)
			      -1))
		  1
		  nil))))

;;(DEFUN COEF MACRO (POL) (SUBST (CADR POL) (QUOTE DEG)
;;  '(DISREP (RATQU (POLCOEF (CAR P) DEG) (CDR P)))))

(defmacro coef (pol)
  `(disrep (ratqu (polcoef (car p) ,pol) (cdr p))))

(defun lapsum (&rest args)
  (cons '(mplus) args))

(defun lapprod (&rest args)
  (cons '(mtimes) args))

(defun expo (&rest args)
  (cons '(mexpt) args))

;;;INVERTS P(S)/Q(S) WHERE Q(S) IS IRREDUCIBLE
(defun ilt3 (p)
  (prog (discrim sign a c d e b1 b0 r term1 term2 degr)
     (setq e (disrep (polcoef q 0))
	   d (disrep (polcoef q 1))
	   degr (pdegree q var))
     (and (equal degr 1)
	  (return
	    (simptimes (lapprod
			(disrep p)
			(expo d -1)
			(expo '$%e (lapprod -1 ilt e (expo d -1))))
		       1
		       nil)))
     (setq c (disrep (polcoef q 2)))
     (and (equal degr 2) (go quadratic))
     (and (equal degr 3) (zerop1 c) (zerop1 d)
	  (go cubic))
     (return (list '(%ilt) (div* (disrep p)(disrep q)) ils ilt))
     cubic (setq  a (disrep (polcoef q 3))
		  r (simpnrt (div* e a) 3))
     (setq d (div* (disrep p)(lapprod a (lapsum
					 (expo ils 3)(expo '%r 3)))))
     (return (ilt0 (maxima-substitute r '%r ($partfrac d ils))))
     quadratic (setq b0 (coef 0) b1 (coef 1))

     (setq discrim
	   (simplus (lapsum
		     (lapprod 4 e c)
		     (lapprod -1 d d))
		    1
		    nil))
     (setq sign (cond ((free discrim '$%i) (asksign discrim)) (t '$positive))
	   term1 '(%cos)
	   term2 '(%sin))
     (setq degr (expo '$%e (lapprod ilt d (power c -1) '((rat) -1 2))))
     (cond ((eq sign '$zero)
	    (return (simptimes (lapprod degr (lapsum (div* b1 c)
						     (lapprod
						      (div* (lapsum (lapprod 2 b0 c) (lapprod -1 b1 d))
							    (lapprod 2 c c)) ilt))) 1 nil))
	    )		   ((eq sign '$negative)
	    (setq term1 '(%cosh)
		  term2 '(%sinh)
		  discrim (simptimes (lapprod -1 discrim) 1 t))))
     (setq discrim (simpnrt discrim 2))
     (setq sign
      (simptimes
       (lapprod
	(lapsum
	 (lapprod 2 b0 c)
	 (lapprod -1 b1 d))
	(expo discrim -1))
       1
       nil))
     (setq c (power c -1))
     (setq discrim (simptimes (lapprod
			       discrim
			       ilt
			       '((rat) 1 2)
			       c)
			      1
			      t))
     (return
       (simptimes
	(lapprod c degr
	 (lapsum
	  (lapprod b1 (list term1 discrim))
	  (lapprod sign (list term2 discrim))))
	1
	nil))))

(declare-top (unspecial ils ilt *nounl* q ratform var
			varlist z))
