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D.15.21.11 twist
Procedure from library tateProdCplxNegGrad.lib (see tateProdCplxNegGrad_lib).
- Usage:
- twist(M,c); M module, c intvec
- Purpose:
- twists the module M by c
- Assume:
- M is a multigraded module
- Return:
- M with the new grading
Example:
| | LIB "tateProdCplxNegGrad.lib";
intvec c = 1,1;
def (S,E) = productOfProjectiveSpaces(c);
setring(S);
module M = freemodule(2);
intmat gradeM[2][2] = 0,1,0,1;
M = setModuleGrading(M,gradeM);
getModuleGrading(M);
==> 0,1,
==> 0,1
intvec c = 2,2;
==> // ** redefining c (intvec c = 2,2;) ./examples/twist.sing:9
module Mtwist = twist(M,c);
getModuleGrading(Mtwist);
==> -2,-1,
==> -2,-1
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