search

clawpack / riemann_book

An interactive book about the Riemann problem for hyperbolic PDEs, using Jupyter notebooks.
BSD 3-Clause "New" or "Revised" License
264 stars 95 forks source link

Characteristics incorrectly terminate in SW section 1.4.5 #152

Closed ketch closed 5 years ago

ketch commented 6 years ago

This refers to the example with the entropy-violating rarefaction imposed in the dam-break problem. The text says that that the 2-characteristics cross within the 2-rarefaction, but something has been changed with the characteristic plotting so that the characteristics coming from the left actually terminate at the left edge of the rarefaction. I don't know when this was changed.

ketch commented 5 years ago

Okay, I tracked this behavior back to this commit, where we made reval return nans inside the unphysical rarefaction:

https://github.com/clawpack/riemann_book/commit/d39b7e2f19aec4a3202ef4848aa446a6e99bd76c

I decided the simplest approach is just to modify the text, which now says (incoming PR):

Plot the 2-characteristics and notice that they impinge on the 2-rarefaction; if plotted within the rarefaction, they would cross.