(quote ^,Matrix,Array)

f^[i,j,k] -- extract some rows of blocks from a matrix f.

The target of f should be a direct sum, and the result is obtained by composition with the projection onto the sum of the components numbered i, j, k. Free modules are regarded as direct sums.

i1 : f = map(ZZ^2 ++ ZZ^2, ZZ^2, {{1,2},{3,4},{5,6},{7,8}})



o1 = | 1 2 |

     | 3 4 |

     | 5 6 |

     | 7 8 |



              4        2

o1 : Matrix ZZ  <--- ZZ

i2 : f^[0]



o2 = | 1 2 |

     | 3 4 |



              2        2

o2 : Matrix ZZ  <--- ZZ

i3 : f^[1]



o3 = | 5 6 |

     | 7 8 |



              2        2

o3 : Matrix ZZ  <--- ZZ

i4 : f^[1,0]



o4 = | 5 6 |

     | 7 8 |

     | 1 2 |

     | 3 4 |



              4        2

o4 : Matrix ZZ  <--- ZZ

See also submatrix, Module ^ Array, and Matrix _ Array.