affinePart -- Replaces columns in a matrix with an identity matrix

• Usage:

  affinePart(M,L)

  affinePart(M,n)

• Inputs:
  • M, a matrix,
  • L, a list,
  • n, an integer,
• Outputs:
  • a matrix,

i1 : S=ZZ[a_1..a_8];

i2 : M=matrix{toList(a_1..a_4),toList(a_5..a_8)}

o2 = | a_1 a_2 a_3 a_4 |
     | a_5 a_6 a_7 a_8 |

             2      4
o2 : Matrix S  <-- S

i3 : affinePart(M,{0,2})

o3 = | 1 a_2 0 a_4 |
     | 0 a_6 1 a_8 |

             2      4
o3 : Matrix S  <-- S