Matrix _ {...} -- get some columns from a matrix

Matrix _ {...} -- get some columns from a matrix

Synopsis:

Operator: _

Input:

an instance of class Matrix.

an instance of class List.

Output:

an instance of class Matrix.

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 of 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];

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

See also:

Code:

     -- ../../../Macaulay2/m2/matrix.m2:404-408
     Matrix _ List := Matrix => (f,v) -> (
          v = splice v;
          listZ v;
          submatrix(f,v)
          )