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copied!<p>Variables in MATLAB are passed using "call by value" (<a href="http://www.mathworks.com/support/solutions/en/data/1-15SO4/?solution=1-15SO4">with some exceptions</a>), so any value that you pass to a function and modify has to be returned from the function and either placed in a new variable or the old variable overwritten. Returning the value of a variable from a function is simple: you just place the variable name in the <a href="http://www.mathworks.com/help/techdoc/matlab_prog/bresuxt-1.html#br67dei-1">output argument list</a> for the function.</p> <p>For your example, you would do this:</p> <pre><code>function A = test(A) A = test1(A); %# Overwrite A with value returned from test1 A = test2(A); %# Overwrite A with value returned from test2 end function A = test1(A) %# Pass in A and return a modified A #% Modify A end function A = test2(A) %# Pass in A and return a modified A #% Modify A end </code></pre> <p>One thing to be aware of is <a href="http://www.mathworks.com/help/techdoc/matlab_prog/f0-38052.html#f0-38068">variable scope</a>. Every function has its own workspace to store its own local variables, so there are actually 3 unique <code>A</code> variables in the above example: one in the workspace of <code>test</code>, one in the workspace of <code>test1</code>, and one in the workspace of <code>test2</code>. Just because they are named the same doesn't mean they all share the same value.</p> <p>For example, when you call <code>test1</code> from <code>test</code>, the value stored in the variable <code>A</code> in <code>test</code> is copied to the variable <code>A</code> in <code>test1</code>. When <code>test1</code> modifies its local copy of <code>A</code>, the value of <code>A</code> in <code>test</code> is unchanged. To update the value of <code>A</code> in <code>test</code>, the return value from <code>test1</code> has to be copied to it.</p>

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