# Doesnt overwrite Variable inside of Loop

조회 수: 2(최근 30일)
Raz134 2021년 1월 21일
편집: Stephen 2021년 1월 22일
I am trying to overwrite the variable "anzahl_gamma" when gamma on the position t is equal to "g_s", g_s is 0.05
so "anzahl_gamma" should be 4 after my loop but it doesnt overwrite.
gamma = [0.005,0.01,0.025,0.0500,0.1,0.9,0.95,0.975,0.99,0.995];
signifikanzniveau = 0.95;
g_s = 1 - signifikanzniveau; % 0.05
anzahl_gamma=0;
for t = 1:10
if gamma(t)== g_s
anzahl_gamma = t;
end
end
Why does this give me anzahl_gamma=0;
and when i change g_s to 0.05 directly it works:
for t=1:10
if gamma(t)==0.05
anzahl_gamma=t;
end
end
with 0.05 directly i get anzahl_gamma=4;
What am i missing here? why is the first one (gamma(t)==g_s) not working?

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### 채택된 답변

Matt Gaidica 2021년 1월 22일
편집: Matt Gaidica 2021년 1월 22일
gamma = int32([0.005,0.01,0.025,0.0500,0.1,0.9,0.95,0.975,0.99,0.995] * 1000);
signifikanzniveau = 0.95;
g_s = int32((1 - signifikanzniveau) * 1000); % 0.05
anzahl_gamma = 0;
for t = 1:10
if gamma(t) == g_s
anzahl_gamma = t;
end
end
There are a few ways to solve this. See here about floating point numbers. Also, beware gamma is a reserved function, I try to stay away from using those as variable names.
##### 댓글 수: 2표시숨기기 이전 댓글 수: 1
Stephen 2021년 1월 22일
"I didnt know that matlab cannot compare vectors if they do not consist of integer numbers"
It can. But operations on the binary floating point numbers that your computer hardware supports (and that enable MATLAB to perform very fast and efficient HW operations for many numeric computations) by their very nature accumulate floating point error. This is simply a feature of binary floating point numbers.
It is up to the programmer to understand the behaviors of binary floating point numbers. For example, Iinstead of testing for exact equality, the recommended approach is to compare the absolute difference against a tolerance:
abs(A-B)<tol
This is worth reading as well:

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