Change default numeric type to float in matlab

Question

Matlab by default uses double as the numeric type. I am training a GMM and running out of memory, so I want to change the default numeric type to float which takes half the memory as double. Is it possible?

I know that single(A) converts a double precision element A to single precision but we need to allocate double precision storage for A first which runs out of memory. Also, I cannot use single() around all my matrix allocation as various functions in many toolboxes are called which I cannot change manually.

So is there a way that calling zeros(n) will allocate a matrix of floats by default instead of double ?

Answer 1

No, there is currently no way to change the default numeric type to float / single. See these informative posts on MathWorks forums:

• http://www.mathworks.com/matlabcentral/answers/8727-single-precision-by-default-lots-of-auxiliary-variables-to-cast
• http://www.mathworks.com/matlabcentral/answers/9591-is-there-a-way-to-change-matlab-defaults-so-that-all-workspace-floating-point-values-to-be-stored-i

Also, quoting John D'Errico on the first link I referenced - a formidable and legendary MATLAB expert:

This is not possible in MATLAB. Anyway, it is rarely a good idea to work in single. It is actually slower in many cases anyway. The memory saved is hardly worth it compared to the risk of the loss in precision. If you absolutely must, use single on only the largest arrays.

As such, you should probably consider reformulating your algorithm if you are using so much memory. If you are solving linear systems that are quite large and there are many zero coefficients, consider using sparse to reduce your memory requirements.

---

Besides which, doing this would be dangerous because there may be functions in other toolboxes that rely on the fact that double type allocation of matrices is assumed and spontaneously changing these to single may have unintended consequences.

Answer 2

As @rayryeng said, there's no way in MATLAB to "change the default numeric type" to single. I'm not even entirely sure what that would mean.

However, you asked a specific question as well:

So is there a way that calling zeros(n) will allocate a matrix of floats by default instead of double?

Yes - you can use zeros(n, 'single'). That will give you an array of zeros of type single. zeros(n) is just a shorthand for zeros(n, 'double'), and you can ask for any other numeric type you want as well, such as uint8 or int64. The other array creation functions such as ones, rand, randn, NaN, inf, and eye support similar syntaxes.

Note that operations carried out on arrays of single type may not always return outputs of type single (so you may need to subsequently cast them to single), and they may use intermediate arrays that are not of type single (so you may not always get all the memory advantages you might hope for). For example, many functions in Image Processing Toolbox will accept inputs of type single, but will then internally convert to double in order to carry out the operations. The functions from Statistics Toolbox to fit GM models do appear to accept inputs of type single, but I don't know what they do internally.