Re: [FLASH-BUGS] avisco bug for cylindrical coords

From: Tomasz Plewa (tomek@flash.uchicago.edu)
Date: Wed Aug 27 2003 - 08:53:37 CDT

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    Thanks, Andrew. We will immediately include safeguards to prevent
    it from happening.

    Tomek 

    --
On Wed, Aug 27, 2003 at 01:51:45AM -0700, Andrew MacFadyen wrote:
> 
> In cylindrical coordinates with a reflecting boundary for the radial 
> coordinate and xmin = 0.0, x(i-1) = -x(i) for i = 5 so x(5)**2 = x(4)**2 
> and there is a division by zero for i = 5 in the computation of avis(i).
> avis(5) is set to zero anyway in hydro_1d for reflecting b.c. but the 
> following change avoids the divide by zero.
> 
> 
> --- ../../source/hydro/explicit/split/ppm/avisco.F90    2003-06-10 
> 12:31:23.000000000 -0700
> +++ avisco.F90  2003-08-26 18:09:09.000000000 -0700
> @@ -58,8 +58,12 @@
> 
>       if (igeomx == 1) then
>          do i = 5, nzn4+1
> -           avis(i) = (x(i) * u(i) - x(i-1) * u(i-1)) * 2.0 /    &
> -                (x(i)**2 - x(i-1)**2)
> +           IF (x(i)**2 == x(i-1)**2) THEN
> +              avis(i) = 0.0
> +           ELSE
> +              avis(i) = (x(i) * u(i) - x(i-1) * u(i-1)) * 2.0 /    &
> +                   (x(i)**2 - x(i-1)**2)
> +           ENDIF
>             avis(i) = - cvisc * avis(i) * (x(i) - x(i-1))
>          enddo
>       end if
> 
> 
> -- 
> Andrew MacFadyen 
> http://www.its.caltech.edu/~aim
> Theoretical Astrophysics, Caltech 
> andrew@tapir.caltech.edu
> MC 130-33, Pasadena, CA 91125    (626): 796-5675(fax); 395-8413(w); 
> 396-8247(h)
> 
> 

    --

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