function y = jinc(x);

# usage: jinc(x)
#
# This function is the equivalent of sinc (cardinal sinus) in the plane,
# it yields the radial component of the Fourier transform of a disc.
# The 1st zero is 3.8317

x(x==0) = 0.00001;
#y = sin(x)./x.^3 -cos(x)./x.^2;
y = 2* besselj(1,x)./x;
endfunction

# nshow(ifftshift(fft2(fftshift( jinc(3*abs(Ip-(1+1i)/51.2)))))/1.7823)
