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.
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