explicitly pass parameter by reference

Young Zhou — Mon, 06 Oct 2008 16:20:21 -0400

I want to know how to pass parameters by reference? I need to pass and big chunk of data to a function, and this function does not change data.

I found an article (http://www.mathworks.com/support/solutions/data/1-15SO4.html?solution=1-15SO4) which states that Matlab will determine whether to pass by value or pass by reference automatically. I just want to confirm it.

Re: explicitly pass parameter by reference

Steven Lord — Mon, 06 Oct 2008 17:07:26 -0400

"Young Zhou" <predicate_zy@yahoo.com> wrote in message
news:gcdds5$o8j$1@fred.mathworks.com...
>I want to know how to pass parameters by reference? I need to pass and big
>chunk of data to a function, and this function does not change data.

You cannot, unless your parameter is an instance of a handle class.

> I found an article
> (http://www.mathworks.com/support/solutions/data/1-15SO4.html?solution=1-15SO4)
> which states that Matlab will determine whether to pass by value or pass
> by reference automatically. I just want to confirm it.

MATLAB uses copy-on-write, which means that if you don't change the data
inside your function, it will not be copied into the workspace of the
function. For instance, in:

function y = myfunction(x)
y = x(1);

you're not writing to x, so even if x is very large it won't be copied into
the workspace. You can see this:

% open whatever memory profiling tool you want
% on Windows, you can use Task Manager.
% on other platforms, you can use "top"
% When you execute this command, the memory usage of MATLAB should increase
significantly
x = ones(10000);
% When you execute this command, it shouldn't.
y = myfunction(x);

--
Steve Lord
slord@mathworks.com

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