create a complex array with fake imaginary part?

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Dehuan
Dehuan 2014-12-23
编辑： Matt J 2014-12-25
Hi, everyone,
I want to create a complex array but with real values. I tried things like b=(complex(a)), but it turns out that imaginary part does not exist. Then I pass the array to a mex function, and the mex runs a mxGetPi and fails because the imaginary part is not allocated, then it crashes.
Is there a way to fake a complex array in matlab with imaginary part allocated?
Thanks
Dehuan

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回答（3 个）

Matt J
Matt J 2014-12-23
编辑：Matt J 2014-12-23
The only thing that comes to mind is to add a hopefully negligible non-zero imaginary part to one of the elements,
a(k)=a(k)+eps(a(k))*i;
Note that only one imaginary element in the array needs to be non-zero in order for mxGetPi to see an imaginary part. You might be able to be strategic about your choice of k, depending on what your application is doing.
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Dehuan
Dehuan 2014-12-24
The reason is as simple as "One can not make his/her boss to change his/her code because he/she want to use it in a hacked/ugly way."
Matt J
Matt J 2014-12-24
编辑：Matt J 2014-12-24
"One can not make his/her boss to change his/her code because he/she want to use it in a hacked/ugly way."
Your boss' code is already ugly if it can't handle strictly real input data. Imagine an fft() routine that could only handle a signal with a non-zero imaginary part.
I would find a diplomatic way to tell him/her that, and offer to upgrade the code as we've described.

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Matt J
Matt J 2014-12-24
编辑：Matt J 2014-12-24
This might be wishful thinking, but if the operation f() to be performed by the MEX is linear, you could leverage that,
f(a) = f(a+b*i)+f(a-b*i)
where b is any fake non-zero imaginary data that you wish to add.
Matt J
Matt J 2014-12-24
编辑：Matt J 2014-12-25
You could try creating your own mex function that appends a zero imaginary part to a real int16 input. If you use mxCreateNumericArray with the ComplexFlag argument set to true, I think there's a chance that it will let you allocate a zero imaginary part.
You would need to use the conversion tool in the very last step, just before the input needs to be fed to your boss' mex code.

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