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

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

[Torsten]

u3 = max(eps,u3)

?

Answer 1

[Vilém Frynta]

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.

[Rahul]

ok Sir. I will do that.

[Rahul]

Can you plz advice how to implement it only in column 3 of my matrix?

with regards

[Vilém Frynta]

Depends on the position of the columns, but I'll show you.

Also, please, accept my answer if it was useful for 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

Answer 2

[E. Cheynet]

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.

[Rahul]

May be its a numerical error in pdepe solver?

[E. Cheynet]

The error comes likely from the function that calculate the turbulence intensity.