[Octave-bug-tracker] [bug #39314] convn(x, y, "valid") produces results that are different from Matlab

[Mike Miller]

Update of bug #39314 (project octave):

              Item Group:        Incorrect Result => Inaccurate Result      
                  Status:                    None => Confirmed              
                 Release:                   3.6.4 => dev                    
                 Summary: The convn() function produces results that are
different from Matlab. => convn(x,y,"valid") produces results that are
different from Matlab

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Follow-up Comment #1:

Thank you for your bug report. Confirmed, also present in the development
version of Octave. Note that the error you are seeing is present only in the
"valid" mode of the convn function (and possibly conv2).

The error can also be observed this way (using your provided dataset for this
example):


y1 = convn (zzz, hhh, "full")(8:12, 8:12, 5);
y2 = convn (zzz, hhh, "same")(4:8, 4:8, 3);
y3 = convn (zzz, hhh, "valid");
assert (y2, y1);
assert (y3, y1);


This shows that it is an error in how the "valid" convolution subset is
computed. The "full" and "same" operations give the same result (within a much
tighter tolerance) as the conv2d matrix you have supplied that was generated
by Matlab.

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