Create function handle from function file

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Arthur Roué 2020-3-10

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评论： tommsch 2020-11-30

Is it possible to create a function handle from function file ? In other words, create a function_handle object @foo from file foo.m.

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Star Strider 2020-3-10

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编辑：Steven Lord 2020-3-10

在 MATLAB Online 中打开

Yes!

In some instances, that is necessary in order to evaluate the function.

Example —

    function y = f(x)
        y = x.^2 - 2;
    end

fz = fzero(@f,1)

produces:

fz =
     1.4142

A reference: What Is a Function Handle?

[SL: typo fix]

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Steven Lord 2020-3-11

在 MATLAB Online 中打开

The function for which you want to create the function handle must be in scope when the function handle is created. It does not need to be in scope when the function handle is evaluated.

function fh = myTimesThree
fh = @localTimesThree;
    function y = localTimesThree(x)
        y = 3*x;
    end
end

You can run myTimesThree then call the function handle it returns even though (because it is a local function inside the file) you couldn't call localTimesThree directly.

f = myTimesThree;
y1 = f(1:10)
y2 = localTimesThree(1:10) % Throws an error

So if you made the function not on the path in scope to MATLAB temporarily (by using cd or addpath) and created the function handle while it was in scope, you could then call that function using the function handle even if you've changed back to a different directory and/or restored the previous path.

Arthur ROUÉ -- I'm curious why you're running the tests in a separate MATLAB session. If your runTests function is a wrapper around the built-in runtests function that's part of the unit testing framework included in MATLAB you could specify the tests input to runtests as the name of the folder containing your tests.

Arthur Roué 2020-3-11

Thanks for your answer Steven Lord, it's a nice way to call a function not in scope.

I do use the testsuite call to run my tests. The reason why I run it in a separate MATLAB session is because I also loop on MATLAB versions to ensure the compatibility ot the toolbox I created in several MATLAB versions.

tommsch 2020-11-30

@Steven Lord

The function for which you want to create the function handle must be in scope when the function handle is created. It does not need to be in scope when the function handle is evaluated.

When the function is shadowed by another function later on, the function handle may point to another function.

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