f_{i,j}

f_{i,j,k,...} -- produce the submatrix of a matrix f consisting of columns numbered i, j, k, ... .

Repetitions of the indices are allowed.

If the list if column indices is a permutation of 0 .. n-1, where n is the number of columns, then the result is the corresponding permutation of the columns of f.

     i1 = R = ZZ/101[a..f]
     
     o1 = R
     
     o1 : PolynomialRing

     i2 = p = matrix {{a,b,c},{d,e,f}}
     
     o2 = | a b c |
          | d e f |
     
                  2       3
     o2 : Matrix R  <--- R

     i3 = p_{1}
     
     o3 = | b |
          | e |
     
                  2       1
     o3 : Matrix R  <--- R

     i4 = p_{1,1,2}
     
     o4 = | b b c |
          | e e f |
     
                  2       3
     o4 : Matrix R  <--- R

     i5 = p_{2,1,0}
     
     o5 = | c b a |
          | f e d |
     
                  2       3
     o5 : Matrix R  <--- R