Math behind code doing ifft of padded fft and more

Question

accf=fft([zeros(1000,3);acc;zeros(1000,3)]);

cutoff1=0;

X1=[0,0,0;
               zeros(round((size(accf,1)-1)/2*cutoff1/50),3);  %% 50 ??
               ones(ceil((size(accf,1)-1)/2)-round((size(accf,1)-1)/2*cutoff1/50),3);
               ones(floor((size(accf,1)-1)/2)-round((size(accf,1)-1)/2*cutoff1/50),3);
               zeros(round((size(accf,1)-1)/2*cutoff1/50),3)];

X2=angle(accf);

X=X1.*exp(X2*sqrt(-1));

acc=real(ifft(X));

acc=acc(1001:end-1000,:);

I guess this is some kind of filtering. Can you help me to find the reference materials for the math?

Answer 1

This makes little sense.

1. it zero pads the input on both sides and does an FFT
2. it generates a matrix of the same size with all ones except for the first first row which is zero
3. It copies the phase of the FFT result to the matrix of ones
4. It does an inverse FFT

So it's simply the inverse FFT of the input signal but with the magnitude set 1 (other than DC which is 0)

I'm guessing that this is supposed to generate some sort of rectangular mask window but with setting cutoff1 = 0 it's all just ones and there is really no reason to create the matrix in such a tortured way. You could simply do X1 = ones(size(accf)); X1(1,:) = 0;