[ET Trac] #2647: incorrect WENO coefficient in GRHydro WENO reconstruction code

[Roland Haas]

#2647: incorrect WENO coefficient in GRHydro WENO reconstruction code

 Reporter: Roland Haas
   Status: open
Milestone: 
  Version: 
     Type: bug
 Priority: major
Component: EinsteinToolkit thorn

Comment (by Roland Haas):

In case it helps, the “average to left” matrix that one needs is the product of the “average to center” and “center to left” matrices show in the WHAM paper. And in Maple code this would be:

```
with(linalg);
C_cl := matrix([[15/8, -5/4, 3/8], [3/8, 3/4, -1/8], [-1/8, 3/4, 3/8]]);
C_ac := matrix([[23/24, 1/12, -1/24],[-1/24, 13/12, -1/24],[-1/24, 1/12, 23/24]]);
C_al := multiply(C_cl, C_ac);
```

which gives:

```
       [ 11/6  -7/6   1/3 ]
C_al = [  1/3   5/6  -1/6 ]
       [ -1/6   5/6   1/3 ]
```

which is almost what shows up in the code. The matrix is used in the code. Except that the code sorts by a different index \(see comment “ these are from equ. \(18\) and \(19\) when substituting into each other and sorting by the index i-r\+j”\).

--
Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2647/incorrect-weno-coefficient-in-grhydro-weno
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