How do I initialize a complex array to zeros in MATLAB?

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MathWorks Support Team 2012-5-18

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https://ww2.mathworks.cn/matlabcentral/answers/94599-how-do-i-initialize-a-complex-array-to-zeros-in-matlab

编辑： Royi Avital 2020-12-29

MATLAB documentation recommends that pre-allocation of variables speeds up performance. I would like to pre-allocate a complex array in my code to zeros. However, when I type the following commands:

x = zeros(100,1) + j*zeros(100,1);

MATLAB creates a 100-by-1 real double array. I would like to create a complex array and initialize both the real and imaginary parts to zeros.

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Answer 1

MathWorks Support Team 2012-5-18

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https://ww2.mathworks.cn/matlabcentral/answers/94599-how-do-i-initialize-a-complex-array-to-zeros-in-matlab#answer_103951

A complex number can be created in MATLAB using the COMPLEX function. To initialize a complex number with zero as the real part and non-zero imaginary part, enter the following at the MATLAB command prompt

a = zeros(1,100);
x = complex(a,0);

To verify that the above command actually creates a 100-by-1 complex array, enter the following at the MATLAB command prompt

whos x

If you were to create the complex arrary with the above code and then assign a pure real number to one part of x or perform an arithmetic operation with a real number, MATLAB will de-allocate the complex part of the variable x . Type the following commands to observe this behavior:

x = x + 1.0;
whos x

When a real number, 1.0 was added to x, MATLAB de-allocates the complex part of the variable x and creates a 100-by-1 real double array. To keep the complex part, wrap COMPLEX around the expression.

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James Tursa 2016-11-10

编辑：James Tursa 2016-11-10

You did an operation that resulted in the imaginary part of z being identically 0. MATLAB detected this result and deallocated the imaginary part. So you would have to follow this up with:

z = complex(z)

I think TMW comments were meant to be interpreted as a whole array assignment. E.g.,

x = complex(x + 1.0);

Qu Cao 2017-1-9