wkb@cbnews.ATT.COM (Wm. Keith Brummett) (04/21/89)
I have need of a small, fast routine in C language that will invert
matrices of order <= 4. (Actually, I'll take a large, slow one that
does order 2 or 3). Does anyone have something like this that they
would care to send me? If it matters, it will be used in a small
graphics project.
BTW, can anyone tell me why it is that every language except C seems
to have standard subroutines to do this?
Thanks in advance!
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`----------------------------------------------------------------------'k1wolcot@pikes.Colorado.EDU (Kenneth A. Wolcott) (04/21/89)
In article <5785@cbnews.ATT.COM>, wkb@cbnews.ATT.COM (Wm. Keith Brummett) writes: [ ... lines deleted ... ] > BTW, can anyone tell me why it is that every language except C seems > to have standard subroutines to do this? [ ... lines deleted ... ] I did not see any matrix inversion routines "BUILT-IN" since I started in Pascal in 1981 -- let's see -- I've looked at, used or read about as many as twenty different PC-based or mini-computer Pascal compilers -- none had matrix inversion routines! Ada doesn't have one (and people accuse Ada of being the "kitchen-sink" language) -- I must have missed it when I looked at Prime Pl/1 -- I don't think any of our 7 FORTRAN compilers have it... I think that you are after a LIBRARY function (not BUILT-IN) for matrix inversion. If so, that is a installation-dependent characteristic! Someone at site #1 has a FORTRAN compiler on a PC with that library -- someone at site #2 has the same compiler and the same hardware, but doesn't have that library. Same thing with "C". Same thing with Ada, Pascal, Modula-2, PL/1, COBOL -- you name the language -- you'll find different libraries installed. ANSI never (I don't think so) did standardize the libraries for each language! How could it be done? It might be real nice to be able to go to six different sites and get identical library support! Kenneth A. Wolcott University of Colorado at Denver Computing Services Advising & Operations "k1wolcot@pikes.colorado.edu" or "kwolcott@pikes.colorado.edu" or "kwolcott@copper.colorado.edu" or "kwolcott@orphan.colorado.edu" or "kawolcott@cudenver.bitnet" ==========================================================================
gwyn@smoke.BRL.MIL (Doug Gwyn) (04/21/89)
In article <5785@cbnews.ATT.COM> wkb@cbnews.ATT.COM (Wm. Keith Brummett) writes: > I have need of a small, fast routine in C language that will invert > matrices of order <= 4. /* The following do not attempt to handle singularities or ill-conditioning. */ void Inv1( double a[1][1], double b[1][1] ) { b[0][0] = 1.0 / a[0][0]; } void Inv2( double a[2][2], double b[2][2] ) { register double d = a[0][0] * a[1][1] - a[0][1] * a[1][0]; b[0][0] = a[1][1] / d; b[0][1] = -a[1][0] / d; b[1][0] = -a[0][1] / d; b[1][1] = a[0][0] / d; } void Inv3( double a[3][3], double b[3][3] ) { double m00 = a[1][1] * a[2][2] - a[2][1] * a[1][2]; double m01 = a[1][2] * a[2][0] - a[2][2] * a[1][0]; double m02 = a[1][0] * a[2][1] - a[2][0] * a[1][1]; register double d = a[0][0] * m00 + a[0][1] * m01 + a[0][2] * m02; b[0][0] = m00 / d; b[0][1] = m01 / d; b[0][2] = m01 / d; b[1][0] = (a[2][1] * a[0][2] - a[0][1] * a[2][2]) / d; b[1][1] = (a[2][2] * a[0][0] - a[0][2] * a[2][0]) / d; b[1][2] = (a[2][0] * a[0][1] - a[0][0] * a[2][1]) / d; b[2][0] = (a[0][1] * a[1][2] - a[1][1] * a[0][2]) / d; b[2][1] = (a[0][2] * a[1][0] - a[1][2] * a[0][0]) / d; b[2][2] = (a[0][0] * a[1][1] - a[1][0] * a[0][1]) / d; } void Inv4( double a[4][4], double b[4][4] ) { /* XXX -- you provide this yourself, I'm getting tired */ } > BTW, can anyone tell me why it is that every language except C seems > to have standard subroutines to do this? Very few languages have standard matrix inversion functions. APL is about the only one I know of. Certainly not Fortran or Pascal.