I look on NR the exemple file dftint, this usage
polint, realft, four1,dftcor.

this exemple with input f(x) to integrate, return the integrals of function
f(x)*cos(wx) and f(x)*sin(wx) .

is possible have integrals of only f(x) ?


(i test it for simple function f(x) and check with qgauss (f(x)*cos(wx))
but the precision is 1 order worst.)