Ramón Casero Cañas on Tue, 7 Jan 2003 01:03:19 +0100 (MET) |
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inverse of a modulo 2 matrix |
Hi, I'm Ramón, rcasero@tsc.uc3m.es; our mail server has been down for the whole Christmas, so I have to use this address meanwhile. > 1) To inverse a matrix, use A^-1 or 1/A. > > 2) If A is invertible, you should rather use matsolve() than matinverseimage(). > > 3) matsolve(A,X) is faster than computing A^-1, but not much, so you are right, > it is best to compute A^-1 if you have many vectors X. Thanks, Bill. I tried this in GP, and it worked. I actually did this ----------------------------------- ? a=[Mod(0,2),Mod(1,2); Mod(1,2),Mod(1,2)] %2 = [Mod(0, 2) Mod(1, 2)] [Mod(1, 2) Mod(1, 2)] ? a^(-1) %3 = [Mod(1, 2) Mod(1, 2)] [Mod(1, 2) Mod(0, 2)] ? a^(-1)*a %4 = [Mod(1, 2) Mod(0, 2)] [Mod(0, 2) Mod(1, 2)] -------------------------------- Why? Because I want to invert a modulo 2 matrix, and then use it to span modulo 2 vectors. I know that I can work with reals and do a^(-1) = inv(a) * det(a) but I would like to stay in {0, 1}. Maybe pari can do this, and this is the reason of my interest in inversing a matrix. But I would like to do this with a function, using the C interface, not the gp program. The inversion function is what I cannot find in the documentation (I did find the data type for the modulo 2 symbols). Happy New Year, Ramón. -- +++ GMX - Mail, Messaging & more http://www.gmx.net +++ NEU: Mit GMX ins Internet. Rund um die Uhr für 1 ct/ Min. surfen!