Printing variables for debugging

General
1

Hi all,

I'm currently working with Peter and Antony on implementing enthalpy damping into PyFR to reduce the start up period.

Could anyone tell me how to print the content of a PyFR variable in the console or in an output file for debugging?

Thanks in advance for your help!

Cheers,

Kevin

2

Hi Kevin,

I'm currently working with Peter and Antony on implementing enthalpy
damping into PyFR to reduce the start up period.

Could anyone tell me how to print the content of a PyFR variable in
the console or in an output file for debugging?

It depends what you mean by a "PyFR variable". If this is simply a
Python variable then you can use a regular Python print statement to
output it to the console. Alternatively, if you are only running with a
single MPI rank you can drop into IPython:

  import IPython; IPython.embed()

which is often easier and more convenient as you can "look around" and
see exactly what is going on.

Otherwise, if it is a variable in a kernel things are a little bit more
difficult. When it comes to debugging "kernels" (and I use the term
loosely!) I am inclined to agree with Linus Torvalds on the issue [1].
All of the kernels in PyFR were written without the use of either a
debugger or print statements. If you're being careful you shouldn't
need either.

However, although officially not supported, you can on occasion utilise
printf(...) inside of the CUDA and C/OpenMP backends. I must warn you
that this is not officially supported and is known to break under a wide
range of circumstances. Caveat emptor...

If outside of the kernel/macro definition you put:

#include <stdio.h>

you should be able to---inside of your kernel/macro---do

printf("%f\n", myvar);

of course the order in which these printf statements come out to the
console is effectively random.

Regards, Freddie.

[1] linus-im-a-bastard-speech

3

Hi Freddie,

Thank you for you answer, it does work.

I also had a look at the link you shared, which was an interesting reading. Don't worry, I don't plan on printing everything all the time.

Thank you once more for your time.

Best,

Kevin