Bill Allombert on Mon, 11 May 2009 16:10:06 +0200 |
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Re: Another problem with matrix inversion |
On Mon, May 11, 2009 at 09:57:53AM +0200, Jeroen Demeyer wrote: > Lorenz Minder wrote: >> So while A has an inverse in this case, it is not found. The workaround >> using chinese remaindering works if the factorization is known, so this >> is going to be a problem if the modulus is an RSA modulus, for example. >> It would be better to try to run the algorithm as is, and as soon as a >> nonzero non-invertible remainder is found, to split into two instances >> with the now known partial factorization and continue. > > This brings up another question regarding GP: is it possible to trap > "impossible inverse modulo" errors and actually recover the element > which caused the impossible inverse? I think it would be nice to have > that functionality in GP, but I don't really know what would be the > correct way to do it. This is only possible in libpari mode currently, using the variable global_err_data. For GP, this is point 5) of bug #329. Maybe we should add a function errdata() that return the current value of global_err_data. Cheers, Bill.