Evaluate function stored in Matlab cell array

Question

I have a function called objective in Matlab I evaluate by writing [f, df] = objective(x, {@fun1, @fun2, ..., @funN}) in a script. The functions fun1, fun2, ..., funN have the format [f, df] = funN(x).

Inside objective I want to, for each input in my cell array called fun, evaluate the given functions using the Matlab built-in function feval as:

function [f, df] = objective(x, fun)
f  = 0;
df = 0;
for i = 1:length(fun)
    fhandle   = fun(i);
    [fi, dfi] = feval(fhandle, x);
    f         = f + fi;
    df        = df + dfi;
end
end

I get the following error evaluating my objective.

Error using feval
Argument must contain a string or function_handle.

I do not get how to come around this error.

score 3 · Accepted Answer · edited May 23 '17 at 12:28

3

You need to reference the elements of fun using curly braces

fhandle = fun{i};

PS
It is better not to use i and j as variable names in Matlab

Alternatively, a solution using cellfun.

edited May 23 '17 at 12:28

Community

1
1

answered Mar 05 '13 at 11:40

Shai

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Thanks! But why not `i` and `j`? – sehlstrom Mar 05 '13 at 12:08
2

@sehlstrom - see the linked question regarding `i` and `j`. – Shai Mar 05 '13 at 12:40

score 2 · Answer 2 · answered Mar 05 '13 at 13:23

2

A more elegant approach using cellfun

function [f df] = objective( x, fun )
[f, df] = cellfun( @(f) f(x), fun );
f = sum(f);
df = sum(df);

Note the kinky use of cellfun - the cellarray is the fun rather than the data ;-)

answered Mar 05 '13 at 13:23

Shai

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Evaluate function stored in Matlab cell array

2 Answers2