janetResolution -- construct a free resolution for a given ideal or module using Janet bases

Synopsis

• Usage:

  C = janetResolution M

• Inputs:
  • M, a matrix or an ideal or a module
• Outputs:
  • C, a chain complex, a (non-minimal) free resolution of (the module generated by) M

Description

The computed Janet basis for each homological degree can be extracted with janetBasis.

The sets of multiplicative variables can also be extracted from the Janet basis in each homological degree with multVar.

Note that janetResolution can be combined with resolution: when providing the option 'Strategy => Involutive' to resolution, janetResolution constructs the resolution.

i1 : R = QQ[x,y,z];

i2 : M = matrix {{x,y,z}};

             1      3
o2 : Matrix R  <-- R

i3 : C = janetResolution M

      1      3      3      1
o3 = R  <-- R  <-- R  <-- R  <-- 0
                                  
     0      1      2      3      4

o3 : ChainComplex

i4 : janetBasis(C, 2)

     +------+---------+
o4 = || -y ||{z, y, x}|
     ||  x ||         |
     ||  0 ||         |
     +------+---------+
     || -z ||{z, y, x}|
     ||  0 ||         |
     ||  x ||         |
     +------+---------+
     ||  0 ||{z, y}   |
     || -z ||         |
     ||  y ||         |
     +------+---------+

o4 : InvolutiveBasis

i5 : multVar(C, 2)

o5 = {set {x, y, z}, set {x, y, z}, set {y, z}}

o5 : List

i6 : R = QQ[x,y,z];

i7 : I = ideal(x,y,z);

o7 : Ideal of R

i8 : res(I, Strategy => Involutive)

      1      3      3      1
o8 = R  <-- R  <-- R  <-- R  <-- 0
                                  
     0      1      2      3      4

o8 : ChainComplex

See also

• janetBasis -- compute Janet basis for an ideal or a submodule of a free module
• multVar -- extract the sets of multiplicative variables for each generator (in several contexts)
• invSyzygies -- compute involutive basis of syzygies