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

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MathWorks Support Team on 18 May 2012
Edited: Royi Avital on 29 Dec 2020
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.

MathWorks Support Team on 18 May 2012
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.
Qu Cao on 9 Jan 2017
Thank you for clarifying the answer.

Royi Avital on 29 Dec 2020
Edited: Royi Avital on 29 Dec 2020
In later versions one could do something like vB = zeros(3, 1, 'like', 1j);.

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