Synopsis
		sfcurv2 < in.rsf > out.rsf slope=slope.rsf niter=5 m=1 n=1 interp=

Parameters
		string interp= interpolation method: maxflat lagrange bspline   int m=1 b[-m, ... ,n]   int n=1 b[-m, ... ,n]   int niter=5 iterations   file slope= auxiliary output file name