Matrix _ List -- select columns

• Operator: _

• Usage:

  f_cols

• Inputs:
  • f, a matrix, a matrix between free modules
  • cols, a list, a list of integers denoting the choice of columns
• Outputs:
  • a matrix, the submatrix of f corresponding to the columns cols.

i1 : R = QQ[a..f];

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_{1,2,0}

o4 = | b c a |
     | e f d |

             2      3
o4 : Matrix R  <-- R