Re: [OctDev] No isimag() curioso

[Michael D G. <mic...@gm...>]

On 09/07/2012 05:30 PM, Daniel J Sebald wrote:
> In working with the fftfilt() routine and wanting to know if the 
> inputs were purely imaginary I wondered why there is no such thing as 
> isimag().  It seems as though it would be as useful as or more useful 
> than iscomplex().
>
> Here's the thing: iscomplex() appears to be simply the complement of 
> isreal(), unless I'm missing a more sophisticated use of syntax:
>
> octave:5> x = 1
> x =  1
> octave:6> [isreal(x) iscomplex(x)]
> ans =
>
>    1   0
>
> octave:7> x = i
> x =  0 + 1i
> octave:8> [isreal(x) iscomplex(x)]
> ans =
>
>    0   1
>
> octave:9> x = 1+i
> x =  1 + 1i
> octave:10> [isreal(x) iscomplex(x)]
> ans =
>
>    0   1
>
> octave:11>
>
> I ask, What's the point of having a function that is simply !isreal()? 
> On the other hand isimag(), which is equivalent to "all (real (x) == 
> 0)) && !isreal (x)", would be a nice shorthand.
>
> Just an observation.  Usually duplication of function (or its 
> complement) is weeded out of programming languages.
>
> Dan 
I also recently noticed some quirks with complex:
x = 1 + 0i   is treated as real and not complex.
but
x = 0 + 1i  is treated as imag and complex.

But, this is consistent with Matlab.  However, Matlab has no iscomplex 
and also
differs in its example for help isreal.  There, Matlab gives an example:
        x = magic(3);
        y = complex(x);

which gives:
 >> y

y =

      8     1     6
      3     5     7
      4     9     2
 >> isreal(y)

ans =

      0
but, ~isreal(y) gives:
ans =

      1

The text in the help messages says that
isreal(y) returns
     false, because COMPLEX returns y with an all zero imaginary
     part.
-------------------------------------------
but Octave gives:

y =

    8 + 0i   1 + 0i   6 + 0i
    3 + 0i   5 + 0i   7 + 0i
    4 + 0i   9 + 0i   2 + 0i

and:
octave:21> isreal(y)
ans = 0
and:
octave:29> ~isreal(y)
ans =  1

The only difference is in the display of y.
This hardly qualifies as a bug, but does add a bit
to the confusion.  Some people would imagine
that real and imaginary would be treated "symmetrically."

So far I do not see much point in making a change.