Why do I keep getting the error message array indices must be positive integers or logical values?

Array indices must be positive integers or logical values.

Error in Drift (line 12)
X(h) = X(0) + mu*h + sigma*Z;

for the following code...

T = 10;
N = 100;
h = T/N;
mu = 0.1;
sigma = 0.2;
X = zeros(1,N+1);
for k = 1:100
for i = 1:N+1
Z = normrnd(0,h);
X(h) = X(0) + mu*h + sigma*Z;
end
plot(Time,X);
hold on
end

[John D'Errico]

MATLAB has an index origin of 1, not 0. So X(0) will fail, and give you exactly that error.

Answer 1

[Matt J]

Looks like this line was accidentally using C-indexing syntax.

X(i) = X(1) + mu*h*(i-1) + sigma*Z;

Answer 2

[John D'Errico]

MATLAB has an index origin of 1, not 0. So X(0) will fail, and give you exactly that error. (Matt pointed that out.)

But also

T = 10;
N = 100;
h = T/N;
...
    
X = zeros(1,N+1);

X(h) = X(0) + mu*h + sigma*Z;

What is h? h=10/100 = 0.1.

X is a vector. Can you index a vector at the 0.1 location? Where is that? Sort of between location 0 (which does not even exist in MATLAB anyway) and memory location 1?

Sorry. Start with the getting started tutorials. You need to learn how MATLAB does indexing.

Answer 3

[Catalytic]

Why do I keep getting the error message array indices must be positive integers

Because the h in X(h) is non-integer and the 0 in X(0) is non-positive.