function [b,a]=u_chb2ap(N,As,Omegac);
[z,p,k]=cheb2ap(N,As);
      a=real(poly(p));
    aNn=a(N+1);
      p=p*Omegac;
      a=real(poly(p));
    aNu=a(N+1);
    b=real(poly(z));
    M=length(b);
    bNn=b(M);
    z=z*Omegac;
    b=real(poly(z));
    bNu=b(M);
    k=k*(aNu*bNn)/(aNn*bNu);
    b0=k;
    b=k*b;