MATLAB: Does FPRINTF put minus signs in front of zeros in the file

MATLABminusnegativezeros

Why does FPRINTF put minus signs in front of zeros in my file?
MATLAB states that these values are really zero, so it's not a round off error.

Best Answer

This is a result of 0 and -0 having different IEEE representations. The following example MATLAB code illustrates this difference:
>> format hex
>> [0 -0]
 ans =
    0000000000000000   8000000000000000
When MATLAB calls FPRINTF, MATLAB actually calls a C routine which treats them differently. However, despite this difference, MATLAB treats 0 and -0 the same in all calculations (ie. 0 == -0). Therefore you can work around this behavior by replacing '-0' with 0 in MATLAB, as shown in the following example:
m = [0 -0]
fprintf(1,'m = [%1.2f %1.2f]\n',m)
m(m==0) = 0
fprintf(1,'m = [%1.2f %1.2f]\n',m)
 m =
      0     0
 m = [0.00 -0.00]
 m =
      0     0
 m = [0.00 0.00]
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