RingElement

RingElement _ {...}

Synopsis:

Usage: g = f_d

Operator: _

Input:

f, an instance of class RingElement: a polynomial

d, an instance of class List: a list of integers

Output:

g, an instance of class RingElement: the sum of those terms of f whose multi-degree is d.

The length of d should be the same as the degree length of f.

See also:

RingElement _ ZZ

degreeLength -- the number of degrees

Code:

     -- ../../../Macaulay2/m2/enginering.m2:214-220
     RingElement _ List := RingElement => (f,d) -> (
          if degreeLength ring f =!= #d
          then error ("degree length of ring element doesn't match specified degree");
          u := select(terms f, t -> d === degree t);
          if #u === 0 then 0_(ring f)
          else sum u
          )