MATLAB Programming Fundamentals - MathWorks

Use Nested Functions to Pass Fewer Arguments

When working with large data sets, be aware that MATLAB makes a temporary copy of an

input variable if the called function modifies its value. This temporarily doubles the

memory required to store the array, which causes MATLAB to generate an error if

sufficient memory is not available.

One way to use less memory in this situation is to use nested functions. A nested function

shares the workspace of all outer functions, giving the nested function access to data

outside of its usual scope. In the example shown here, nested function setrowval has

direct access to the workspace of the outer function myfun, making it unnecessary to

pass a copy of the variable in the function call. When setrowval modifies the value of A,

it modifies it in the workspace of the calling function. There is no need to use additional

memory to hold a separate array for the function being called, and there also is no need

to return the modified value of A:

function myfun

A = magic(500);

function setrowval(row, value)

A(row,:) = value;

end

setrowval(400, 0);

disp('The new value of A(399:401,1:10) is')

A(399:401,1:10)

end

Using Appropriate Data Storage

MATLAB provides you with different sizes of data classes, such as double and uint8, so

you do not need to use large classes to store your smaller segments of data. For example,

it takes 7 KB less memory to store 1,000 small unsigned integer values using the uint8

class than it does with double.

Use the Appropriate Numeric Class

The numeric class you should use in MATLAB depends on your intended actions. The

default class double gives the best precision, but requires 8 bytes per element of

memory to store. If you intend to perform complicated math such as linear algebra, you

must use a floating-point class such as a double or single. The single class requires

29 Memory Usage