How to for loop through a function?

So I have the code below which generates coordinates for a 2D airfoil. It takes a inputs such as CST_no_tail([-1 -1 -1], [1 1 1],100) and outputs a [101,2] array of x and y coordinates. This part works fine.

function [coord] = CST_no_tail(wl,wu,N);
%CST_no_tail([-1 -1 -1], [1 1 1],100) - Running this in  command works fine


% Description : Create a set of airfoil coordinates using CST parametrization method 
% Input  : wl = CST weight of lower surface
%          wu = CST weight of upper surface
%          dz = trailing edge thickness
% Output : coord = set of x-y coordinates of airfoil generated by CST


% Create x coordinate
x=ones(N+1,1);y=zeros(N+1,1);zeta=zeros(N+1,1);
for i=1:N+1
    zeta(i)=2*pi/N*(i-1);
    x(i)=0.5*(cos(zeta(i))+1);
end

% N1 and N2 parameters (N1 = 0.5 and N2 = 1 for airfoil shape)
N1 = 0.5;
N2 = 0.5;

zerind = find(x(:,1) == 0); % Used to separate upper and lower surfaces

xl= x(1:zerind-1); % Lower surface x-coordinates
xu = x(zerind:end); % Upper surface x-coordinates

[yl] = ClassShape(wl,xl,N1,N2); % Call ClassShape function to determine lower surface y-coordinates
[yu] = ClassShape(wu,xu,N1,N2);  % Call ClassShape function to determine upper surface y-coordinates

y = [yl;yu]; % Combine upper and lower y coordinates

coord = [x, y]; % Combine x and y into single output

%% Function to calculate class and shape function
function [y] = ClassShape(w,x,N1,N2);


% Class function; taking input of N1 and N2
for i = 1:size(x,1)
    C(i,1) = x(i)^N1*((1-x(i))^N2);
end

% Shape function; using Bernstein Polynomials
n = size(w,2)-1; % Order of Bernstein polynomials

for i = 1:n+1
     K(i) = factorial(n)/(factorial(i-1)*(factorial((n)-(i-1))));
end

for i = 1:size(x,1)
    S(i,1) = 0;
    for j = 1:n+1
        S(i,1) = S(i,1) + w(j)*K(j)*x(i)^(j-1)*((1-x(i))^(n-(j-1)));
    end
end

% Calculate y output
for i = 1:size(x,1)
   y(i,1) = C(i,1)*S(i,1) + x(i);
end

I'm trying to compare multiple inputs so I want to loop through a matrix of multiple inputs, running each iteration through the function.

Can someone explain why my method below doesn't work?

ar = {[-1 -1 -1] [1 1 1] 100;
    [-0.5 -1 -1] [0.5 1 1] 100;
    [-1 -1 -0.5] [1 1 0.5] 100;
    [-0.5 -1 -0.5] [0.5 1 0.5] 100
    }
    
% create coord array
shapes_list = zeros(101,2, length(ar));

for j = 1:length(ar);
    shapes_list(:,:,j) = CST_no_tail(ar{j,:})   %should take output coord and insert it insto
end

It looks like output of the for loop isnt the same as the quivalent cell but I'm not sure why?

For example inserting the first row of ar into the function works fine - CST_no_tail([-1 -1 -1], [1 1 1],100)

However when inserting the row from the matrix doesnt work - CST_no_tail(ar(1))

Answer 1

[Sindar]

To pass/access the elements in a cell array, you need {}. () accesses the cell. Check the difference between what returns from

ar(1)

and

ar{1}

[Nason Zikayo]

Thanks for the response.

Trying both commands, they both return only the first element in each input array.

So ar(1) and ar{1} both return -1 -1 -1.

I want the whole of the input array [-1 -1 -1] [1 1 1] 100.

How do I get this?

[Sindar]

Ah, I didn't look too closely. The issue is that you are not passing an array as input, but rather three separate variables. Luckily, you can do this with your cell array easily:

shapes_list(:,:,j) = CST_airfoil(ar{j,:})

This will pass the jth row of ar, expanded as three input arguments

[Nason Zikayo]

No worries, your solution worked fine the first time, but all subsequent tries in the following error.

Out of memory. The likely cause is an infinite recursion within the program.

Running this code after the code in the post:

for j = 1:length(ar);
%ar{j,:}
shapes_list(:,:,j) = CST_no_tail(ar{j,:})
end

I am really confused as why it seems to work sometimes but not others. I've tried restarting matlab and clearning workspace but I'm getting the same error.

Thanks for your time.

[Sindar]

Hmm, my suggestion would be to add a breakpoint (https://www.mathworks.com/help/matlab/matlab_prog/debugging-process-and-features.html) or just pause after it's run for a bit, and see where it seems to be recursive. Also, check that n is what you expect, since the factorials might be to blame.

Also, is it supposed to be calling CST_no_tail(ar{j,:}) or CST_airfoil(ar{j,:})?

[Nason Zikayo]

Thanks for the link, this looks like a really useful debugging feature.

Error in CST_no_tail (line 28)
[yl] = ClassShape(wl,xl,N1,N2); % Call ClassShape function to determine lower surface y-coordinates

Checking this I can see that after completing the classshape with the input wl = [-1 -1 -1] or ar{1,1}, the function never moves on to line 29 (which takes wu or ar {1,2}). Instead line 28 is repeatedly exectuted after completion despite a valid output being recieved. Not sure why this is as from my understanding, once line 28 executes and yl is recived it should move on to execute line 29.

CST_no_tail(ar{j,:}) should be called, I've fixed the code in the post if you wanted to recreate the error.

[Sindar]

Try running line-by-line, seeing what runs (also check the variable sizes in case it isn't a recursion that's the problem)