fix the bound for the coeffs of minpoly #2480
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the bounds computed in _fmpz_mat_bound_ovals_of_cassini did not match the reference. There exists an explicit 12x12 matrix where the bounds were too small by a factor (bit length) of 2, hence the minpoly was wrong.
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|
badMat.txt |
without the fix of the bounds, "small" matrices with "huge" entries will run into the error. Experimentally, for 2x2 matrices around 4500 bits would have triggered the problem.
| fmpz_sub(v1 + i, v1 + i, fmpz_mat_entry(op, i, j)); | ||
| } | ||
| } | ||
| /* |A|^t * |A| * [1,1,...,1]^T */ |
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The code doesn't seem to match the formula in the comment. It looks like v1[i] is being repeatedly multiplied by different matrix entries while the intended behavior is to repeatedly add products of different matrix entries.
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good catch...I've tried again, with a better matrix vector product
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the bounds computed in _fmpz_mat_bound_ovals_of_cassini did not match the reference. There exists an explicit 12x12 matrix where the bounds were too small by a factor (bit length) of 2, hence the minpoly was wrong.