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From: gregc@cgl.ucsf.edu (Greg Couch)
Newsgroups: comp.lang.postscript
Subject: invertmatrix
Message-ID: <13887@cgl.ucsf.EDU>
Date: 3 May 90 00:05:37 GMT
References: <@tfd.UUCP> <5903@amelia.nas.nasa.gov>
Sender: daemon@cgl.ucsf.edu
Reply-To: gregc@cgl.ucsf.edu.UUCP (Greg Couch)
Organization: Computer Graphics Lab, UCSF
Lines: 37
Followup-To:

In article <5903@amelia.nas.nasa.gov> izen@amelia.nas.nasa.gov (Prof. Steven H. Izen) writes:
>If anyone wants to implement a version of invertmatrix for us SGI users,
>please post it.

I posted this before (April 1989) in comp.windows.news and since 4sight is
close to NeWS 1.1, this should work for SGI users too.

	- Greg Couch
	gregc@cgl.ucsf.edu

%!
% The following is an implementation of the PostScript invertmatrix for NeWS.
% No copyright allowed.  Greg Couch, UCSF Computer Graphic Lab, April 1989
%
% [ a b c d x y ] ->
%	[ d -b -c a (cy - dx) -(ay - bx) ] / (ad - bc)

systemdict /invertmatrix known not {
	systemdict
	/invertmatrix {	% matrix1 matrix2 invertmatrix matrix2
		7 dict begin
			exch aload pop			% m2 a b c d x y
			/y exch def /x exch def		% m2 a b c d
			/d exch def /c exch def		% m2 a b
			/b exch def /a exch def		% m2
			/t a d mul b c mul sub def	% t = ad - bc
			d t div				% m2 a2
			b neg t div			% m2 a2 b2
			c neg t div			% m2 a2 b2 c2
			a t div				% m2 a2 b2 c2 d2
			c y mul d x mul sub t div	% m2 a2 b2 c2 d2 x2
			b x mul a y mul sub t div	% m2 a2 b2 c2 d2 x2 y2
			7 -1 roll			% a2 b2 c2 d2 x2 y2 m2
			astore				% m2
		end
	} put
} if