DPCM encoder et decoder FOR DC COEFFICIENTS (in JPEG compression)

Hi, What is the coding and decoding of DPCM for DC coefficients for jpeg image compression ?? I am using matlab R2011b. I've got this code (for coding) from mathworks but I can’t decode it. help me plz…

% DPCM FOR DC COEFFICIENTS 
a=1;
for i=1:8:size(luma,1);% luma: Luminance image original 
  for j=1:8:size(luma,2)
      temp141(1:8,a:a+7)=temp1(i:i+7,j:j+7);% temp1: luma after the quantization
      a=a+8;
  end
end

cnt=2;
for i=1:8:size(temp141,2)-7
       temp121=temp141(1,i);%  copy first element of the first 8x8 block 
       if i==size(temp141,2)-7
           break;
       else
       i=i+8;% increment along column to point to the 1st element of the 2nd 8x8 block
       end
       temp131=temp141(1,i);  % copy the first element of  the 2nd 8x8 block 
       dpcm1(cnt,1)=temp131-temp121 % subtract the 2nd element from the first element 
       cnt=cnt+1;                                 

         i=i-8;                           % decrement the column index 

end