The minimum of a matrix

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So I have been writing some code using Sage, which by the way is awesome so far. And I had some simple check to do, i.e. all elements of some matrices have to be nonnegative. So I figured I would just see if the minimum of these matrices is nonnegative. In programms like matlab this is usualy achieved by min(min(A)) for some matrix A. I figured it would be the same for sage, so I tested this to be sure and everything seemed to work. But then I stumbeled upon something weird and I found this case (that is this is some of the output of the case). These are the 5 matrices followed by the minima of the same 5 matrices respectively.

[ 1.0000 0.00000 0.00000 0.00000 0.00000]
[0.00000  3.0000 0.00000 0.00000 0.00000]
[0.00000 0.00000  10.000 0.00000 0.00000]
[0.00000 0.00000 0.00000  5.0000 0.00000]
[0.00000 0.00000 0.00000 0.00000  1.0000]
-------------------------------------------------------------
[ 0.00000   1.0000  0.00000  0.00000  0.00000]
[  1.0000   1.0000  0.00000  0.00000   1.0000]
[ 0.00000  0.00000   4.4444   5.5556  0.00000]
[ 0.00000  0.00000   5.5556 -0.55556  0.00000]
[ 0.00000   1.0000  0.00000  0.00000  0.00000]
-------------------------------------------------------------
[0.00000 0.00000  1.0000 0.00000 0.00000]
[0.00000 0.00000  1.3333  1.6667 0.00000]
[ 1.0000  1.3333  4.4444  2.2222  1.0000]
[0.00000  1.6667  2.2222  1.1111 0.00000]
[0.00000 0.00000  1.0000 0.00000 0.00000]
-------------------------------------------------------------
[ 0.00000  0.00000  0.00000   1.0000  0.00000]
[ 0.00000  0.00000   3.3333 -0.33333  0.00000]
[ 0.00000   3.3333   4.4444   2.2222  0.00000]
[  1.0000 -0.33333   2.2222   1.1111   1.0000]
[ 0.00000  0.00000  0.00000   1.0000  0.00000]
-------------------------------------------------------------
[0.00000 0.00000 0.00000 0.00000  1.0000]
[0.00000  3.0000 0.00000 0.00000 0.00000]
[0.00000 0.00000  10.000 0.00000 0.00000]
[0.00000 0.00000 0.00000  5.0000 0.00000]
[ 1.0000 0.00000 0.00000 0.00000 0.00000]
-----minima--------------------------------------------------
[0, 0, 0, 0, 0]

Now I actually have a case which is very similar, that is, it is a permutation of these set of matrices above and for those I do get the correct answers

[ 1.0000 0.00000 0.00000 0.00000 0.00000]
[0.00000  3.0000 0.00000 0.00000 0.00000]
[0.00000 0.00000  5.0000 0.00000 0.00000]
[0.00000 0.00000 0.00000  10.000 0.00000]
[0.00000 0.00000 0.00000 0.00000  1.0000]
-------------------------------------------------------------
[ 0.00000   1.0000  0.00000  0.00000  0.00000]
[  1.0000   1.0000  0.00000  0.00000   1.0000]
[ 0.00000  0.00000 -0.55556   5.5556  0.00000]
[ 0.00000  0.00000   5.5556   4 ...