How do I call a function handle with an vector - rather than a list of arguments

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JP Hadden 2019-11-20

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https://ww2.mathworks.cn/matlabcentral/answers/492112-how-do-i-call-a-function-handle-with-an-vector-rather-than-a-list-of-arguments

评论： JP Hadden 2019-11-26

Hi,

I was wondering how to call a function handle with an vector of inputs - rather than the list of aguments.

So if I have a function handle which is defined: (I guess it will be clear that I am working on fitting functions here)

fitFunctionHandle = @(a1, wG1, x1,a2, wG2, x2, c, x)(FitGaussianFn(x, [a1, 0, wG1, x1]) +FitGaussianFn(x, [a2, 0, wG2, x2]) + c

And I have an vector of inputs to hand to it

a1Init = 1
wG1Init = 2
x1Init = 3
a2Init = 4
wG2Init = 5
x2Init = 6
a2Init = 7
x = 8
%startPoint = [a1Init, wG1, x1,a2, wG2, x2, c]
inputArray = [a1Init, wG1, x1,a2, wG2, x2, c, x]

How do I call it with the vector startPoint as the input. If I try (for example)

fitFunctionHandle(inputArray)

I get an Error:

Not enough input arguments.

That makes sense since it is expecting 8 inputs rather than a 8 element vector - but I'm wondering whether there is a way of calling it like that. I think for example in python you can convert an array to a list or something.

I'm aware that I could simplify things in this example case where I have a list of known inputs so I could just do:

fitFunctionHandle(a1Init, wG1, x1,a2, wG2, x2, c, x)

or

fitFunctionHandle(inputArray(1),inputArray(2),inputArray(3,inputArray(4), inputArray(5), inputArray(6),inputArray(7),inputArray(8)) 

BUT! I guess I'm trying to allow for expansion where I don't know how many arguments there would be.

For bonus points (again since I'm working on fitting functions) - It would be cool to know how to call it when x is a vector as well. I suspect that I would be doing something like

arrayfunc(fitFunctionHandle([startPoint,x]), xVector)

Thanks in advance for your help.

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Answer 1

Stephen23 2019-11-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/492112-how-do-i-call-a-function-handle-with-an-vector-rather-than-a-list-of-arguments#answer_402403

编辑：Stephen23 2019-11-20

Easy: first define a cell array:

C = {a1Init, wG1, x1,a2, wG2, x2, c, x};

and then use a comma-separated list:

fitFunctionHandle(C{:})

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JP Hadden 2019-11-26

Thanks for your help.... That got me quite far along the way.... What I came up with in the end was...

inputArgCell=num2cell(options.startPoint);
inputArgCell{length(inputArgCell)+1} = xData;
yDataInitialGuess = fitFunction(inputArgCell{:});

As you say it seems like the fitFunction can handle the startingpoint guesses being each 1x1, and the xData being 1xN. (or maybe Nx1).

I'm not sure I fully understand the parameterizing suggestion.

I am basically attempting to define a multi peak fit function to pass to Matlab's nonlinear fit function. The fit function is sort-of bolted together from several other functions in string format - which is then evaluated as a function handle. Probably there are better ways to do it - but I was trying to make it fairly general - eg to allow different types of fit function, and different numbers of peaks - and this is what I've come up with for now...

If I'm being dumb - and I fully expect there are better ways - then let me know.

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