sum() doesn't adjust fixpoint wordlength

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Lennart 2015-6-18

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https://ww2.mathworks.cn/matlabcentral/answers/224416-sum-doesn-t-adjust-fixpoint-wordlength

Hi there,

I am currently facing the problem that the sum() function doesn't adjust the word length of my fixpoint variable although the summode is set to FullPrecision

Here is the code of trouble:

    shiftValue = max(shifts(i,:));
    while max(shiftValue) ~= min(shifts(i,:))-1
        sameShifts = find(shifts(i,:) ==shiftValue)  %coordinates of max shifts
  -->   sigOut_fix(i) = (sigOut_fix(i) + sum(sigInLut(i,sameShifts)))*2^(-1); 
        shiftValue = shiftValue - 1 %reduce the targeted shifting Value
    end

The arrow point at the line that doesn't work properly. sameShifts is a vector with coordinates.

I tried it in the command window on the following example, which worked perfectly fine:

 x = fi(1: 100, true, 16, 0);
 b = fi(3,true,16,0);
 a =  5 : 50;
 y = fi(0,true,16,0); 
 y = (b+sum(x(a)))*2^(-1)

After the last row y's word length is grown to 44 as it should be. But why doesn't it work in my while loop? Is this just a bug or am I missing something?

Any help is highly appreciated!

Thanks in advance!