c ************************************************* c spectrum.f c c gcc-4.1.0 compliation command: c c gfortran spectrum.f c c ************************************************* parameter(eta=0.01) parameter(x0=4.0) parameter(n0=100) c declare some variables complex. complex g,z,zz c open output file. open(7,file="output.dat",status="new") c compute frequency increment. x=n0 dx=x0/x c compute number of bins. n=n0*2 c loop over frequencies. do 2 j=1,n x=dx*(j-n0-0.5) c for this frequency compute green's function. z=cmplx(x,eta) zz=z**2-2.0 g=csqrt(zz**2-4.0) y=aimag(g)*x if(y.gt.0.0) g=-g g=(g+zz)/2.0 c write result to file. write(7,1) x,g 1 format(3f10.4) 2 continue stop end