> On 10/15/2017 12:41 PM, Mark Ma wrote: 
> > 
> > Now the projection of initial values (rewrite the code by manually 
> assemble 
> > the matrix and system_rhs and calculate) run OK, but the time updating 
> of T is 
> > not correct, same phenomenon appears. I believe this may arise from the 
> fact 
> > that direct using matrix vmult (i.e. 
> > | 
> > mass_matrix_T.vmult (system_rhs,old_solution_T_cal); 
> > | 
> > 
> > ) instead of assembling and distribute_local_to_global again may ignore 
> > eliminating the constraint points in matrix or vector, when using 
> > constriantMatrix and interporate_boundary_values to apply the boundary 
> > condition, I am now checking of this. 
>
> So when you visualize the solution, the error is at the boundary but it 
> looks 
> correct in the interior? 
>
> Yes, it is. Thereafter, the error at boundaries does propagate and then 
interfere with the interior. 

>
> > Is there a simple way to update the RHS of old value using something 
> simple 
> > like vmult? 
>
> What is the equation you are trying to implement? 
>
> I am trying just the Heat equation,
rho * C * dT/dt = nabla *(kappba nalbaT) + f(x,y,t);
Boundary condition is,
T(x,y,z,t) = 300K, at boundaries.
 

> Best 
>   W. 
>
> -- 
> ------------------------------------------------------------------------ 
> Wolfgang Bangerth          email:                 bang...@colostate.edu 
> <javascript:> 
>                             www: http://www.math.colostate.edu/~bangerth/ 
>
>

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