[petsc-users] conditioning of snes with dmcomposite & grid sequencing

[Gideon Simpson]

> On Sep 12, 2015, at 4:43 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> 
>    I do not understand. You have the real part of the solution at the origin of u0 stored in the "redundant" part of the DMComposite? What about the on the DMDA mesh? Wouldn't the real part also be there and with the same value? Thus when you interpolate with the solution on the DMDA you would still get the correct values "near" the origin? Hence there is no reason to "involve" the u0 stored in the redundant part in the interpolation?
> 
>  Barry

Suppose my coarse mesh is x1, x2, x3,…, and x0 = 0, corresponds to the origin.  At x0=0, my constraints are that u’(0) = 0, and v(0) = 0.  So u0, the value at the origin, is an unknown that needs to be solved for.  Now, when I do grid sequencing, I ought to be adding a point between x0 and x1, but I don’t, because x0 isn’t part of the DMDA.  
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