bug taking rows of matrices

[David Eisenbud]

I think this is a bug in the facility for taking submatrices in M2:

S = ZZ/101[a,b,c,d]
M = matrix"a,b;c,d"

M_{0,0} -- produces the matrix with two columns equal to the first column of M, as it should
M^{0,0} -- produces a matrix with a row of zeros followed by the first row of M -- wrong!

I came on it (with Jerzy Weyman) when writing a program to compute the sub-pfaffians of a certain size, allowing repetition of the rows and columns ( "permanent(k,M) does it without repetition.)

David

--

David Eisenbud

Professor of Mathematics

University of California Berkeley

www.msri.org/~de

[Mahrud Sayrafi]

I've also noticed a possibly related bug in the target, which is always forced to be free:

S = ZZ/101[a,b,c,d]
N = coker matrix{{3_S},{0}}
m = map(N, , matrix"a,b;c,d")
target m -- N
target m_{0} -- N
target m^{0} -- S^1!!

Mahrud

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