Talk:MUSCL scheme

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Historical perspective[edit]

Maybe, it would be better to illustrate MUSCL more in original context of upwind Godunov schemes, as it is in famous van Leer's serial of papers, and not only in semi-discrete central Godunov schemes, which is quite new concept. But I also use it now in Kurganov-Tadmor variation. --Vladimír Fuka 17:07, 7 September 2006 (UTC)[reply]

Possibly. I will think about it. Griffgruff 11:24, 17 May 2007 (UTC)[reply]

Proper citation[edit]

Proper style of citation in Harvard system (author, date) is not to repeat author's name in parenthesis when it is used in the sentence , for example: ... as shown by Godunov (1959) ... contrary to ... as shown in (Godunov, 1959) ... See http://en.wikipedia.org/wiki/Harvard_system . If you don't mind, I will repair it. --Vladimír Fuka 16:54, 21 October 2006 (UTC)[reply]

Rusanov contribution[edit]

The Kurganov and Tadmor scheme starts with F* reconstruction using the local maximum of the flux jacobian $\partial F/\partial u$ . Isn't this exactly the same as the local Lax-Friedrichs method, originally described by Rusanov in J. Comp. Math. Phys. USSR, 1 (1961)? (Source: Randall J. LeVeque, Finite Volume Methods for Hyperbolic Problems, Cambridge Texts in Applied Mathematics, 2002, see pp. 232,233) --ArthurVanDam 15:25, 14 May 2007 (UTC)[reply]

Yes, you are correct. In fact Kurganov and Tadmor acknowledge this in their paper. I will shortly add someting to this effect. Thank you for your feedback and kind comments on my talk page. Griffgruff 11:22, 17 May 2007 (UTC)[reply]

Reference to Rusanov and local Lax-Friedrichs fluxes now included. Griffgruff 13:37, 18 May 2007 (UTC)[reply]

==Suggestion

I think the comparisons at the end for the analytic and 2nd order and the analytic and 3rd order are nice - but a three way comparison could yield a beter metric of comparison. I think you could use an iSNR analog to indicate the difference between the two approximations. iSNR=10*log_10(norm(analytic-2nd order)/norm(analytic-3rd order)).

Best wishes —Preceding unsigned comment added by 134.134.139.70 (talk) 20:48, 26 July 2010 (UTC)[reply]

Local propagation speed in the KT scheme[edit]

Currently the local propagation speed in the KT scheme is given as

a_{i\pm {\frac {1}{2}}}\left(t\right)=\max \left[\rho \left({\frac {\partial F\left(u_{i}\left(t\right)\right)}{\partial u}}\right),\rho \left({\frac {\partial F\left(u_{i\pm 1}\left(t\right)\right)}{\partial u}}\right),\right]

However, in Eq. (3.2) of the original paper it is defined as

a_{i+{\frac {1}{2}}}\left(t\right)=\max \left[\rho \left({\frac {\partial F\left(u_{i+1/2}^{L}\left(t\right)\right)}{\partial u}}\right),\rho \left({\frac {\partial F\left(u_{i+1/2}^{R}\left(t\right)\right)}{\partial u}}\right),\right]

So instead of using the cell values they use the extrapolated ones. Am I missing something here? Or is this a mistake on the page? Arno Mayrhofer (talk) 04:01, 6 February 2015 (UTC)[reply]

Thank you for spotting this error, which I have now corrected. Graham W. Griffiths (talk) 09:58, 6 February 2015 (UTC)[reply]

Indices in formulas[edit]

In chapter Linear reconstruction

Formula

u_{i+1/2}^{L}=u_{i}+0.5\phi \left(r_{i}\right)\left(u_{i}-u_{i-1}\right),u_{i+1/2}^{R}=u_{i+1}-0.5\phi \left(r_{i}\right)\left(u_{i+1}-u_{i}\right),

should be corrected to

u_{i+1/2}^{L}=u_{i}+0.5\phi \left(r_{i}\right)\left(u_{i+1}-u_{i}\right),u_{i+1/2}^{R}=u_{i+1}-0.5\phi \left(r_{i+1}\right)\left(u_{i+1}-u_{i}\right),

In chapter Example: 1D Euler equations

Formula

\rho _{i+{\frac {1}{2}}}^{L}=\rho _{i}+0.5\phi \left(r_{i}\right)\left(\rho _{i+1}-\rho _{i}\right),\rho _{i+{\frac {1}{2}}}^{R}=\rho _{i+1}-0.5\phi \left(r_{i+1}\right)\left(\rho _{i+2}-\rho _{i+1}\right),

should be corrected to

\rho _{i+{\frac {1}{2}}}^{L}=\rho _{i}+0.5\phi \left(r_{i}\right)\left(\rho _{i+1}-\rho _{i}\right),\rho _{i+{\frac {1}{2}}}^{R}=\rho _{i+1}-0.5\phi \left(r_{i+1}\right)\left(\rho _{i+1}-\rho _{i}\right),

82.206.66.51 (talk) 16:09, 1 February 2016 (UTC)[reply]

I was having issues in my code due to the mistake mentioned just above this comment! After changing the indices in my own program, the time evolution was fixed. I second that these indices should be fixed! 216.165.95.1 (talk) 00:37, 19 February 2017 (UTC)[reply]

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Error in indexes[edit]

Hi all,

I think there is a mistake in the definition of the indexes in the chapter "Linear reconstruction". If I believe the book "Numerical Analysis Using R", the correct version should be

$u_{i+1/2}^{L}=u_{i}+0.5\phi \left(r_{i}\right)\left(u_{i+1}-u_{i}\right),u_{i+1/2}^{R}=u_{i+1}-0.5\phi \left(r_{i+1}\right)\left(u_{i+2}-u_{i+1}\right),$

$u_{i-1/2}^{L}=u_{i-1}+0.5\phi \left(r_{i-1}\right)\left(u_{i}-u_{i-1}\right),u_{i-1/2}^{R}=u_{i}-0.5\phi \left(r_{i}\right)\left(u_{i+1}-u_{i}\right),$

with $r_{i}={\frac {u_{i}-u_{i-1}}{u_{i+1}-u_{i}}}.$

With these definitions, one actually has that $u_{{i+1}-1/2}^{R}=u_{i+1/2}^{R}$ , and therefore that $F_{i+{\frac {1}{2}}}^{*}=F_{i+1-{\frac {1}{2}}}^{*}$ , a property that is exploited by the code GEES linked on this page, where only $F_{i+{\frac {1}{2}}}^{*}$ is evaluated. This is not the case with the current version of the wikipage.