Comparing a matrix (list[][]) ?

[jairodsl]

Hi,

How can I find the minus element greater than zero in a matrix, my
matrix is

matrix=
[9,8,12,15],
[0,11,15,18],
[0,0,10,13],
[0,0,0,5]

I dont want to use "min" function because each element in the matrix is
associated to (X,Y) position.

Thanks a lot.

jDSL