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

조회 수: 1(최근 30일)
Thomas Clontz
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
  댓글 수: 1
John D'Errico
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
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;

John D'Errico
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.

Catalytic
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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