Computes the maximum of each column of x, where x
is an integer, real, or double-precision matrix
with at least one row.
The return value is a row vector with the same type and
number of columns as x.
The j-th element of the return value is the maximum of
the elements in the j-th column of x.
If index is present, its input value has no effect.
Its output value is an integer row vector with the same number of columns
The j-th element of the output value of index is the
index of the row containing the maximum element of
the j-th column of x.