void interp(double **uf, double **uc, int nf)
{
	int ic,iif,jc,jf,nc;
	nc=nf/2+1;
	for (jc=1,jf=1;jc<=nc;jc++,jf+=2)
		for (ic=1;ic<=nc;ic++) uf[2*ic-1][jf]=uc[ic][jc];
	for (jf=1;jf<=nf;jf+=2)
		for (iif=2;iif<nf;iif+=2)
			uf[iif][jf]=0.5*(uf[iif+1][jf]+uf[iif-1][jf]);

	for (jf=2;jf<nf;jf+=2)
		for (iif=1;iif <= nf;iif++)
			uf[iif][jf]=0.5*(uf[iif][jf+1]+uf[iif][jf-1]);
}