MATLAB: Passing a mat file variable to a function

.mat filefunctionlarge variableload

I have written a function myfun.m which works on a very large input variable var stored in a file myfile.mat in the current folder. If I first load var into the workspace and then call myfun(var), var requires memory of twice its size because it is kept both in the base and the function workspace. How can I instead pass just the names of myfile.mat and var on calling myfun, and load var from within myfun? Thank you!

Best Answer

A) Just put the call to load the variable in your function, perhaps with a call to uigetfile to enable the user to select the file interactively, or

B) Put the filename in the argument list instead of var and return var (or whatever is the desired result instead of having it in the argument list --

function var_perhaps_modified=myfun(inputfilename)
  ....

or,

C) Use nested functions and then the copy of var can be shared.

Related Solutions

MATLAB: How to programatically make workspace variable name same as the .mat file name loaded into Matlab

A much better approach than awful dynamic variable names is to use simple, efficient indexing, e.g.:

D = 'path to the directory where the files are saved';
S = dir(fullfile(D,'*.mat'));
for k = 1:numel(S)
    F = fullfile(D,S(k).name);
    C = struct2cell(load(F));
    S(k).data = C{1}; % assumes exactly ONE variable per file
end

All of the data will be stored in the structure S:

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

MATLAB: Input to output variable copies in functions : influence on cpu

It does not matter for cpu purposes whether you copy to a variable first and work on the copy, or if you work on the original and copy at the end.

However, in very restricted contexts, there are some cases where

function var_in = complex_function(var_in)
% Lots of operations on var_in %
% ---------------------------- %


% ---------------------------- %
% ---------------------------- %
end

can be faster. Notice the output variable name is the same as the input variable name. When the moon is in the right phase, and the wind is blowing just right, and you are wearing your lucky 5-leaf clover, then this can save making a deep copy of var_in .

Best Answer

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MATLAB: How to programatically make workspace variable name same as the .mat file name loaded into Matlab

MATLAB: Input to output variable copies in functions : influence on cpu

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