CellVariable hasOld() should set self.old

[wd15]

CellVariable hasOld() should set self.old=self.copy() if self.old is None and hasOld was not explicitly set to False in __init__(). This avoids the problem of forgetting to set hasOld=True when using sweep() and then sweep() just iterating forward as if it was a full time step.

Imported from trac ticket #85, created by wd15 on 09-19-2006 at 14:51, last modified: 06-21-2011 at 13:19

[wd15]

I think I mean updateOld() rather than hasOld().

Trac comment by wd15 on 06-20-2011 at 16:34

[wd15]

Setting self._old to be self.copy() in updateOld() leads to some unintended consequences. One possible scenario is this

• hasOld is False on instantiation
• the variable assigns constraints
• an explicit diffusion term is used
• updateOld is then called

The equation will use the old value without the constraints and the constraints won't get seen by the diffusion term (which uses the old value for explicit cases). Changing what var.old is defined as is quite dangerous in this respect and in others. A better option is to just throw an exception if updateOld() is called when hasOld has not been set to True. This is done in r4632.

Trac comment by wd15 on 06-21-2011 at 13:19