[aspect-devel] Updated definition of compressibility

[Wolfgang Bangerth]

All,
up to now, the documentation of the 
MaterialModel::Interface::compressibility() function said that the 
function should return
     d rho/dp
However, (i) this doesn't match the commonly used definition of the word 
compressibility, (ii) the code is actively wrong in that case. 
Consequently, we've changed what the documentation of this function 
says, namely that the function should in fact return
   1/rho  d rho/dp
Incidentally, the only currently implemented compressible model we have 
(Thomas' Table model) already implements these semantics, so no further 
changes are needed as long as you all use the models currently 
implemented in Aspect. Of course, if anyone should have developed their 
own models already you may want to double-check what your function is doing.

Best
  Wolfgang & Timo

-- 
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Wolfgang Bangerth               email:            bangerth at math.tamu.edu
                                 www: http://www.math.tamu.edu/~bangerth/