Can anyone please explain me the Fourier Descriptor coding?

I have the coding for Fourier Descriptor.But i can't able to understand what is happening in some lines. This is the full coding

function [f]= foury(im)
  % input: image in binary form, from which the Fourier Descriptors are     calculated
  % output: Fourier Descriptor ,which describes the shape of the image by calculating Fourier Transform of its  Boundary  

    im = im2bw(im);
    b = bwboundaries(im);
    [max_size, max_index] = max(cellfun('size', b, 1));

    if size(b,1)==0
        c=zeros(10,2);
    else
    c = b{max_index};
    end
    % calculating Fourier Transform of image boundaries
    s = c(:, 1) + 1i*c(:, 2);
    descriptors = fft(s,512);
    descriptors=descriptors';
    D=abs(descriptors(1));
    descriptor=zeros(511,1);

    for i=1:511
      descriptor(i)=abs(descriptors(i+1))/D;
    end

    f = descriptor;
    f = transpose(f);

i want to know the explanation of this part.Please help me

[max_size, max_index] = max(cellfun('size', b, 1));

if size(b,1)==0
    c=zeros(10,2);
else
c = b{max_index};
end