[Octave-bug-tracker] [bug #51556] function isreal applied on complex numbers with zero imaginary part

[John W. Eaton]

Follow-up Comment #2, bug #51556 (project octave):

In Matlab, (and Octave, for compatibility reasons) if you want to create a
complex value with a zero imaginary part, you need to use something like
"complex (r, 0)".  And even then, if you use that value in an expression like
this:


x = complex (12, 0)  %% 12+0i
isreal (x)           %% false
y = 1 + x            %% 13
isreal (y)           %% true


you will get a real value as the final result because of the automatic complex
-> real conversion rules for (nearly all) expression results.

I'm certainly not claiming this is mathematically correct or necessarily the
best programming language design.  But it is the way Matlab works and we have
to do the same for compatibility reasons.  If we didn't, we'd be constantly
getting bug reports that Octave fails on code that works perfectly well in
Matlab.

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