function rhs2=rhs2(tspan,uvt,dummy,kx2,ky2,nx,ny)
u2t=uvt(1:nx*ny); v2t=uvt(nx*ny+1:2*nx*ny);
ut=reshape(u2t,nx,ny); vt=reshape(v2t,nx,ny);
u=ifft2(ut); v=ifft2(vt);

urhs=-(kx2.^2+ky2.^2).*u2t+reshape(fft2(v.^2),nx*ny,1);
vrhs=-(kx2.^2+ky2.^2).*v2t+reshape(fft2(u.^2),nx*ny,1);
rhs2=[urhs; vrhs];