submatrix -- select part of a matrix

submatrix -- select part of a matrix

submatrix(m, rows, cols) -- yields a submatrix of the matrix m.
submatrix(m, cols) -- yields a submatrix of the matrix m.

Yields an r by c matrix, where r is the length of the list of integers rows, and c is the length of the list of integers cols. The (i,j)-th entry of the result is m_(rows_i, cols_j). If necessary, any sequences in the lists are spliced into the list.

i1 : R = ZZ/101[a .. o]



o1 = R



o1 : PolynomialRing

i2 : m = genericMatrix(R, a, 3, 5)



o2 = | a d g j m |

     | b e h k n |

     | c f i l o |



             3       5

o2 : Matrix R  <--- R

i3 : submatrix(m, {1,2,0}, {0..2, 4})



o3 = | b e h n |

     | c f i o |

     | a d g m |



             3       4

o3 : Matrix R  <--- R

If rows or cols is omitted, all the indices are used.

i4 : submatrix(m, {1,2}, )



o4 = | b e h k n |

     | c f i l o |



             2       5

o4 : Matrix R  <--- R

It is an error if any element of rows or cols is out of range.

Ways to use submatrix :

submatrix(Matrix,Sequence,Sequence)

submatrix(Matrix,Sequence,List)

submatrix(Matrix,List)

submatrix(Matrix,List,Sequence)

submatrix(Matrix,List,List)

submatrix(Matrix,List,Nothing)

submatrix(Matrix,Nothing,List)