[Users] Boundary issues solving wave equations with MoL

[Severin Frank]

Thank you Roland for your reply!

In the meanwhile I was  able to solve the issue. I changed my original 
evolution requation

ζ̈=Aζ′+Bζ″+Cζ\ddot{\zeta} = A \zeta' + B \zeta'' +C \zeta into a system 
(1) of

ζ˙=Π\dot{\zeta} = \PiΠ˙=Aζ′+Bζ″+Cζ\dot{\Pi}=A\zeta'+B\zeta''+C\zet I 
wanted to avoid the second-order numerical derivatives by using a system (2)

ζ˙=Π\dot{\zeta}=\PiΠ˙=AH+BH′+Cζ\dot{\Pi}=AH+BH'+C\zetaH˙=Π′\dot{H}=\Pi'which 
was source of the problem. This system is analytically equivalent to the 
one above, but indeed not strongly hyperbolic.

I also had to change the boundaries near the r=0 region of the grid, but 
the main issue was the aforementioned one. System (1) works with the new 
boundary conditions.

Thank you very much!
Best regards,
Severin
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