reducedMatrix -- reduced matrix

i1 : F = GF(4);

i2 : n = 7;

i3 : k = 3;

i4 : L = apply(toList(1..k),j-> apply(toList(1..n),i-> random(F)));

i5 : m=matrix(L)

o5 = | 1 a+1 1   a a a+1 a |
     | 1 a+1 a+1 1 1 1   a |
     | 0 0   a+1 1 1 0   0 |

             3      7
o5 : Matrix F  <-- F

i6 : reducedMatrix(m)

o6 = | 0   0 a+1 1 1 0 0 |
     | 0   0 0   0 0 1 0 |
     | a+1 a 0   0 0 0 1 |

             3      7
o6 : Matrix F  <-- F