Generate a list of array components interpreted as a comma separated list

Hi all,

I want to define a function handle, say

fun = @(C) F(C(1),C(2),C(3),C(4),C(5));

but this C array does not always have the same size and also it's size may get quite large. Thus, I'm looking for a more compact and automated way to write the above expression.

Any ideas?

Thanks!

Answer 1

[James Tursa]

If C can be passed in as a cell array, you could do this:

fun = @(C) F(C{:});

The C{:} part will expand as a comma separated list. However, this may not be practical if the size of C could be "quite large" as you put it. In such a case, it would probably be best for the function F to handle the breakout of C inside the function, rather than forcing the cell elements of C into a comma separated list as explicit arguments.

[Stephen23]

The MATLAB documentation explains three ways to create a comma separate list: write out the variables with commas, from a cell array, or from a structure. This answer, using a cell array, is the simplest solution that fulfills the original question's requirements.

[Apostolos Psaros]

Thanks for the answer. This could be useful in other cases, but it seems to not work in what I'm trying to do. Perhaps, if I show you where I'm trying to apply it, you could have another idea:

c = sym('c', [1 3]);
for i=1:3
    F(i)=i^2*c(1)+i^2*c(2)-i*c(3); % Not important, just an arbitrary function
end
F=matlabFunction(F);
fun = @(C) F(C(1),C(2),C(3)); 
options = optimset('Display', 'off');      
X = fsolve(fun, ones(1, 3), options)

And I want to keep the definition of fun this way and also run fsolve this way (see here why: https://www.mathworks.com/matlabcentral/answers/324229-using-fsolve-with-array-of-symbolic-expressions)

[James Tursa]

Kind of ugly, but you could use eval for this, e.g.

% fun = @(C) F(C(1),C(2),C(3)); 
args = sprintf('C(%d),',1:numel(c));
fun = eval(['@(C)F(' args(1:end-1) ')']);

(This is a kinder, gentler use of eval since it doesn't "pop" variables into the workspace)