function res=fastConv(A,B)
% res=fastConv(A,B)
%
% computes the first half of the convolution between 
% the rows of A and the rows of B (through FFT)

k=size(A,2);
res=real(ifft(fft(A,2*k,2)  .*  fft(B,2*k,2), [], 2));
res(:,k+1:end)=[];