Convert strings to array of function handles

Hi, I'm using the opti platform and for NLP problems I need constraints in the following form:

    nlcon = @(x)  [ a(1)*x(1)^3 - b(2)*x(2);...
                    a(2)*x(2)^3 - b(3)*x(3);...
                    a(3)*x(3)^3 - b(1)*x(1)];

So I have small loop to generate these as strings:

a = [1 2  3];
b = [2 6 4 ];
pile = [];
for i = 1:length(a)
    if i <= length(a)-1
        text = [' a(' num2str(i) ')*x(' num2str(i) ')^3 - b(' num2str(i+1) ')*x(' num2str(i+1) ')'];
    else 
        text = [' a(' num2str(i) ')*x(' num2str(i) ')^3 - b(1)*x(1)'];
    end
    pile =  [pile; text];    
end

And pile is the array of polynomials that i would like to form nlcon out of. Now if display or print pile and copy and past the result back into my script it works, but I'm certain there is a more elegant and efficient method. Cell arrays don't work, or at least I've had no success getting opti to accept them.

Kind regards,

ic_fly2

Answer 1

[José-Luis]

a = [1 2  3];
b = circshift(a,[0 -1]);
all_num = [a;a;b;b];

argument = sprintf('a(%i)*x(%i)^3 - b(%i)*x(%i)\r\n',all_num)

[ic_fly2]

Thank you for the speedy reply, I much prefer your method to getting the loop part, unfortunately the output is still a string, which is not what i need to feed to the list of functions. For some reason matlab does not allow me to allocate rows or elements of the array nlcon individually but when written as a whole it accepts them. So the string still needs to be converted to normal input or however matlab calls that.

[José-Luis]

I am not sure I follow. If you want an array of strings, then you could loop through every a value and generate the string as I show.

If you want to transform a string into a function, please look at str2func().

 doc str2func