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UNINIT - Create an uninitialized variable (like ZEROS but faster)

version (7.24 KB) by James Tursa
UNINIT is similar to ZEROS, except UNINIT returns uninitialized values instead of zero values.


Updated 09 May 2011

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UNINIT is very similar to the ZEROS function, except that UNINIT returns an uninitialized array instead of a zero-filled array. Thus, UNINIT is faster than the ZEROS function for large size arrays. Since the return variable is uninitialized, the user must take care to assign values to the elements before using them. UNINIT is useful for preallocation of an array where you know the elements will be assigned values before using them.

Syntax (nearly identical to the ZEROS function)

B = uninit
B = uninit(n)
B = uninit(m,n)
B = uninit([m n])
B = uninit(m,n,p,...)
B = uninit([m n p ...])
B = uninit(size(A))
B = uninit(m, n,...,classname)
B = uninit([m,n,...],classname)
B = uninit(m, n,...,complexity)
B = uninit([m,n,...],complexity)
B = uninit(m, n,...,classname,complexity)
B = uninit([m,n,...],classname,complexity)


B = uninit
Returns a 1-by-1 scalar uninitialized value.

B = uninit(n)
Returns an n-by-n matrix of uninitialized values. An error message
appears if n is not a scalar.

B = uninit(m,n) or B = uninit([m n])
Returns an m-by-n matrix of uninitialized values.

B = uninit(m,n,p,...) or B = uninit([m n p ...])
Returns an m-by-n-by-p-by-... array of uninitialized values. The
size inputs m, n, p, ... should be nonnegative integers. Negative
integers are treated as 0.

B = uninit(size(A))
Returns an array the same size as A consisting of all uninitialized

If any of the numeric size inputs are empty, they are taken to be 0.

The optional classname argument can be used with any of the above.
classname is a string specifying the data type of the output.
classname can have the following values:
'double', 'single', 'int8', 'uint8', 'int16', 'uint16',
'int32', 'uint32', 'int64', 'uint64', 'logical', or 'char'.
(Note: 'logical' and 'char' are not allowed in the ZEROS function)
The default classname is 'double'.

The optional complexity argument can be used with any of the above.
complexity can be 'real' or 'complex', except that 'logical' and 'char'
outputs cannot be complex. (this option not allowed in the ZEROS function)
The default complexity is 'real'.

UNINIT is typically self building. That is, the first time you call UNINIT, the uninit.m file recognizes that the mex routine needs to be compiled and then the compilation will happen automatically. UNINIT uses the undocumented MATLAB API function mxCreateUninitNumericMatrix. It has been tested in PC WinXP versions R2006b through R2011a, but may not work in future versions or non-PC versions of MATLAB.

Cite As

James Tursa (2020). UNINIT - Create an uninitialized variable (like ZEROS but faster) (, MATLAB Central File Exchange. Retrieved .

Comments and Ratings (5)

Dan Po

looks like a really good idea


I got the following error, any idea?


No supported SDK or compiler was found on this computer.
For a list of supported compilers, see

Error using uninit (line 148)
Unable to compile uninit ... Contact author.

nedjma ALI

Markus Reiband

Absolutly perfect!!!

We were able to greatly improve performance of our scripts because we work with very large matrices. This way of fast allocation memory should become a part of the standard Matlab!

Jonathan Sullivan

This is much faster at allocating memory that zeros, or false. If you do any sort of operation on it, it becomes slower than zeros / false. This is best used for quick allocation of memory when you are about to overwrite the values anyways.

The self-compiler makes it really easy to use. Your just simply hit run, and it will compile itself for you.

Great work!

MATLAB Release Compatibility
Created with R2006b
Compatible with any release
Platform Compatibility
Windows macOS Linux

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