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

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Thomas Clontz 2019년 9월 27일
편집: Catalytic 2019년 9월 27일
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
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John D'Errico 2019년 9월 27일
MATLAB has an index origin of 1, not 0. So X(0) will fail, and give you exactly that error.

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### 답변(3개)

Matt J 2019년 9월 27일
편집: Matt J 2019년 9월 27일
Looks like this line was accidentally using C-indexing syntax.
X(i) = X(1) + mu*h*(i-1) + sigma*Z;
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John D'Errico 2019년 9월 27일
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.
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Catalytic 2019년 9월 27일
편집: Catalytic 2019년 9월 27일
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.

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