Array indices must be positive integers or logical values.

x = (a + (i-1).*h)';

alphax = alpha(x);

f = f(x);

I get error: Array indices must be positive integers or logical value

ive tried storing alpha as another variable, but I don't understand.

Here is the full code:

----------------

function [u,x] = solveHeat(alpha, f, a, b, n, tolerance, maxIterations)
h= (b-a)/(n-1);
i=1:n;

x=(a+ (i-1).*h)';
alphax=alpha(x);
f=f(x);

%define starting value of temperature, u
u= [a; zeros(n-2,1);b]

r(1)=0;
r(n)=0;

Dinverse(2:n-1)=1./(-2alphax(2:n-1).*(h^2));
Dinverse(1)=1;
Dinverse(n)=1;

for s =1:maxItreations
    r(2:n-1)= (u(1:n-2)-(2+alphax(2:n-1).*h^2)).*u(2:n-1)...
        +u(3:n)+(h^2)*f (2:n-1));
    u(2:n-1)=u(2:n-1)-Dinverse(2:n-1').*r(2:n-1)';
    if norm(r)<tol,break,end
    
end

end

code to call function

[u, x] = solveHeat(1, @(x) zeros(size(x)), 1, cosh(1), 20, 1e-6, 2000);
error = norm(u - cosh(x))

[Adam Danz]

What are your inputs?

What is the full copy-pasted error message?

And where does ua and ub come from? They aren't defined in your function.

[As111]

Sorry fixed ua, ub

Inputs: [u, x] = solveHeat(1, @(x) zeros(size(x)), 1, cosh(1), 20, 1e-6, 2000)

Array indices must be positive integers or logical values.

Error in solveHeat (line 9)
alphax = alpha(x);

Answer 1

[Adam Danz]

The error is here

% For position in the column vector
x = (a + (i-1).*h)';
alphax = alpha(x);

You're indexing alpha using vector x. As the error indicates, indices need to be positive integers. Instead, x equals

x =
            1
       1.0286
       1.0572
        . . . 

Also, the alpha input is just 1 so why why would that be indexed in the first place?

Lastly, your last two inputs don't appear in your function so they aren't doing anything.