Passing Matrix using call by reference
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Commented: Vaclav Rimal on 11 Dec 2013
When looking for call-by-reference in matlab I found the Handle-Class. What I don't yet understand is how I use that class on a matrix so that I can pass a reference of the matrix and not the matrix itself.
I know matlab already kind of does this with large matrices, but firstly, I don't know how big my matrices will become, and secondly, I want to make sure it is only with reference, since it is done very often and is a performance critical operation.
Vaclav Rimal on 10 Dec 2013
To really take the advantage of handle class, you would need to create your own class based on the class handle. Create a file called largematrix.m having the following code:
classdef largematrix < handle
Then, you can create an object of that class. The variable representing the object in the workspace is in fact a pointer to the part of memory which stores the object. Running the method myfunc behaves like you probably want. The following commands
a.myfunc; % or myfunc(a), which has the same result
2 2 2 2
2 2 2 2
2 2 2 2
2 2 2 2
Vaclav Rimal on 11 Dec 2013
Daniel, the methods will not be copied, for they are the same for all objects you create (assuming they are the same class). The methods should behave just like ordinary functions. I think this is not what matters. Matlab certainly deals this efficiently.
An issue can arise when you create and delete many instances. This depends on what exactly you want to do and whether you can aviod recreating objects by e.g. overwriting their properties by new values (which wouldn't repeatedly capture and release memory).
More Answers (4)
Yes, using assignin and input name will do that for you
>> test = 'hallo'
Sean de Wolski on 10 Dec 2013
Edited: Sean de Wolski on 10 Dec 2013
What operation are you doing inside of myfunc? Is it elementwise?
If so, MATLAB will do the operation in place if x is named the same everywhere:
x = magic(10);
x = myfunc(x);
function x = myfunc(x)
x = x.^2;
Since the operation is being done in-place, no memory copy will be necessary.
Matlab does not create a copy, until it is really needed. So passing big arrays to functions uses no extra memory, except when you change the big matrix inside the function.
Y = X ; No copy is made, Y is a pointer (a reference to X)
X(1) = 1 % this creates a copy of X inside the workspace of the function. Note that Y is untouched.
Y(1) = 1 ; % this now also creates a copy
Edited: Jos (10584) on 10 Dec 2013
OK. Yes, it is possible. See my second answer.
sixwwwwww on 10 Dec 2013
Define you function as below:
function y = myFunc(x)
y = 2;
then try this in command window:
x = 1;
x = myFunc(x);
It will return you value 2 which you need
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