]> https://gitweb.dealii.org/ - dealii-svn.git/commitdiff
Comment on the project_back_saturation
authorbangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Sat, 28 Oct 2006 00:23:35 +0000 (00:23 +0000)
committerbangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Sat, 28 Oct 2006 00:23:35 +0000 (00:23 +0000)
git-svn-id: https://svn.dealii.org/trunk@14110 0785d39b-7218-0410-832d-ea1e28bc413d

deal.II/examples/step-21/doc/intro.dox

index c8fb3af26addc1f5c919035dd1ab0746bd196fe4..74167d099ac6f7c1e2c40c4b64c3c660aa79ffca 100644 (file)
@@ -359,7 +359,13 @@ easily be verified. (Remember that the saturation corresponds to something
 like the water fraction in the fluid mixture, and therefore must physically be
 between 0 and 1.) On the other hand, if we choose our time step according to
 the criterion listed above, this only happens very very infrequently &mdash;
-in fact only once for the entire run of the program.
+in fact only once for the entire run of the program. However, to be on the
+safe side, however, we run a function <code>project_back_saturation</code> at
+the end of each time step, that simply projects the saturation back onto the
+interval $[0,1]$, should it have gotten out of the physical range. This is
+useful since the functions $\lambda(S)$ and $F(S)$ do not represent anything
+physical outside this range, and we should not expect the program to do
+anything useful once we have negative saturations or ones larger than one.
 
 Note that we will have similar restrictions on the time step also in @ref
 step_23 "step-23" and @ref step_24 "step-24" where we solve the time dependent

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