# How can I restrict a parameter (turbulence intensity) to only positive values?

조회 수: 6 (최근 30일)
Rahul 2023년 5월 8일
댓글: E. Cheynet 2024년 2월 26일
Hello,
I have a code in which the parameter u3 which denotes the turbulence intensity oscillates from positive to negative for each iteration. Since negative turbulence does not have any physical meaning, I hence want to restrict the same to only positive values. I'm finding it difficult to restrict the same in the code.
Can someone guide me please for the above-mentioned.
Please run using the callme.m file.
With regards,
rc
##### 댓글 수: 1이전 댓글 -1개 표시이전 댓글 -1개 숨기기
Torsten 2023년 5월 8일
u3 = max(eps,u3)
?

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### 채택된 답변

Vilém Frynta 2023년 5월 8일
hi,
i took a peek at your code and it's massive. therefore i came just to say that if you have a value, where you only want the positive values, you can do this:
a = -5:1:5; % numbers from -5 to 5
idx = a > 0; % logical vectors, where the values are positive
a(idx) % vector 'a', where the values are positive
ans = 1×5
1 2 3 4 5
p.s.
if you really want help, it's a good practice to copy-paste your code here, as it's easier to access compared to downloading the files, opening them in Matlab and running it.
##### 댓글 수: 3이전 댓글 1개 표시이전 댓글 1개 숨기기
Rahul 2023년 5월 9일
Can you plz advice how to implement it only in column 3 of my matrix?
with regards
Vilém Frynta 2023년 5월 9일
Depends on the position of the columns, but I'll show you.
% Random 5×5 matrix
a = randi(10, [5 5])
a = 5×5
10 4 9 3 7 4 9 8 1 2 8 10 2 6 5 2 8 4 5 1 10 10 3 7 6
% Find where values are higher than 5 in the first 3 columns
idx = a(:,1:3) > 5
idx = 5×3 logical array
1 0 1 0 1 1 1 1 0 0 1 0 1 1 0
% Apply index to the matrix
a(idx)
ans = 9×1
10 8 10 9 10 8 10 9 8

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### 추가 답변 (1개)

E. Cheynet 2023년 5월 9일
Rather than restricting the turbulence intensities to positive values only, I suggest to understand why the turbulence intensity is sometimes negative. Per definition, it should not happen. So there may be something wrong in the code.
##### 댓글 수: 2없음 표시없음 숨기기
Rahul 2023년 5월 9일
May be its a numerical error in pdepe solver?
E. Cheynet 2024년 2월 26일
The error comes likely from the function that calculate the turbulence intensity.

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