factor(Module) -- factor a ZZ-module

Synopsis

Usage:
factor M
Function: factor
Inputs:
- M, a module
Outputs:
- a symbolic expression describing the decomposition of M into a direct sum of principal modules

Description

The ring of M must be ZZ.

In the following example we construct a module with a known (but disguised) factorization.

i1 : f = random(ZZ^6, ZZ^4)

o1 = | 6 6 5 2 |
     | 9 9 6 4 |
     | 4 6 7 7 |
     | 6 8 8 9 |
     | 0 3 3 3 |
     | 0 3 6 2 |

              6        4
o1 : Matrix ZZ  <--- ZZ

i2 : M = subquotient ( f * diagonalMatrix{2,3,8,21}, f * diagonalMatrix{2*11,3*5*13,0,21*5} )

o2 = subquotient (| 12 18 40 42  |, | 132 1170 0 210 |)
                  | 18 27 48 84  |  | 198 1755 0 420 |
                  | 8  18 56 147 |  | 88  1170 0 735 |
                  | 12 24 64 189 |  | 132 1560 0 945 |
                  | 0  9  24 63  |  | 0   585  0 315 |
                  | 0  9  48 42  |  | 0   585  0 210 |

                                 6
o2 : ZZ-module, subquotient of ZZ

i3 : factor M

          ZZ   ZZ    ZZ
o3 = ZZ + -- + -- + ----
           5   11   5*13

o3 : Expression of class Sum