On 19/08/2011 18:57, Sucharit wrote:
I am using Sage to compute homologies of large chain complexes. For this, I need to compute kernels of matrices over GF(2).The attached file testmatrix.sage contains the 128 X 120 matrix that I started with. The first command loads the file. The second command should output a zero vector, but it does not. sage: load testmatrix.sage sage: M.kernel().basis()[0]*M (0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1)
HiI get the same result as you so it does look like a bug. I also tried putting algorithm="generic" into the call and got a different, but also wrong, answer.
Your example seems to be quite special, I'm running an infinite loop generating matrices of the same size over GF(2) and so far the kernel is computed correctly for all of them.
I'm curious what could be causing this so I'll have a look at the code and see if I can see what's going on.
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