[Nek5000-users] Boundary nodes cordinates and random generator

[nek5000-users at lists.mcs.anl.gov]

Yes I need some temporal correlation as well. In fact for me evaluating the complex exponential part is okay, the problem was computational expense for generating random number for 150 modes for theta,Phi,Psi and Alfa. I used the built in function of fortran and I experience Segmentation fault in my computer and when I use the code from Numerical recipes (subroutine ran1) it works well. But I just want to know why this happens and what are the other possible solutions. 

By using the ran1 code from Numerical recipe, 150X4 = 600 random numbers are generated at each time step for the random Fourier mode velocities.

Or is there anyway solutions to cut down the number of random numbers by slightly any change in the Fourier mode?

And finally regarding the co ordinates of the inlet boundary is there any quick way to get it?


Regards

Sijo GEORGE


Your replay for my last question:

But I guess you want some temporal correlation as well, i.e. your modes 
will evolve as a harmonic signal also in time? Typically, we chose a few 
modes (say 150) with random wavenumbers and phases, but then we just 
evolve them in space and time. So the problem is then rather to evaluate 
the complex exponential (i.e. cosine and sine signals) than random numbers.

So in that case, one needs to have a RNG that works well in parallel and 
you can restart a simulation without "kinks".

But if you do not need these properties, I would say that computing 150 
random numbers is not very expensive. I typically use a quite "simple" 
generator from Numerical recipes, just because it is portable and gives 
the same numbers on all machines.

Philipp