Hi Piotr,

Thanks for the feedback.

We can add a note indicating nsteps > 1. But I don’t think nsteps has to be 
even?

Cheers

Peter

Dr Peter Vincent MSci ARCS DIC PhD
Senior Lecturer and EPSRC Early Career Fellow
Department of Aeronautics
Imperial College London
South Kensington
London
SW7 2AZ

email: [email protected]<mailto:[email protected]>
web: 
www.imperial.ac.uk/aeronautics/research/vincentlab/<http://www.imperial.ac.uk/aeronautics/research/vincentlab/>
twitter: @Vincent_Lab<https://twitter.com/#!/Vincent_Lab>

On 28 Apr 2016, at 09:28, Piotr Prusiński 
<[email protected]<mailto:[email protected]>> wrote:

Ok, no question :) Anyway, such an information could be introduced somewhere in 
the manual that the nstep is in fact not an integer but rather an "even 
integer" starting from 2 and then wider explanation like yours.

Best regards,
Piotr

W dniu czwartek, 28 kwietnia 2016 00:11:45 UTC+2 użytkownik Freddie Witherden 
napisał:
Hi Piotr,

On 27/04/2016 05:06, Piotr Prusiński wrote:
> I have just found out a curious thing that when changing the nstep value
> to 1 (unity) in [soln-plugin-residual] closure, the code does not
> produce residuals at all in the output file, a *.csv file is created but
> stays empty.

This is due to the design of the residual plugin which estimates the
residual through:

  residual = (prev_soln - curr_soln) / delta_t

with the plugin itself having two phases: the first phase is run one
time step before we are due to save out the residual and its purpose is
to assign:

self._prev = curr

and then in the second phase (run on the next time step) we actually
compute an approximation to the residual itself.

The problem when nsteps = 1 is that in a single time step we have to
perform both phases.  This confuses the code as it is currently written.

I can certainly update the plugin to support this.  However, generally
speaking nsteps = 1 is extremely frequent in terms of residual output.
Usually, we would not run below nsteps = 50 given that with an explicit
code such as PyFR the time steps themselves are usually extremely small.

Regards, Freddie.


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