Method log

Math/Subset Sum Problem.cpp:218–221

    return ans.mod_xk(n);
  }
  poly log(int n) const { //ln p(x) mod x^n
    assert(a[0] == 1);
    return (differentiate().mod_xk(n) * inverse(n)).integrate().mod_xk(n);
  }
  poly exp(int n) const { //e ^ p(x) mod x^n
    if(is_zero()) return {1};
    assert(a[0] == 0);