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Matrix ^ Array -- select rows of blocks

Synopsis

Description

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