# [aspect-devel] temperature assembly timing

Wolfgang Bangerth bangerth at math.tamu.edu
Thu Sep 19 04:31:38 PDT 2013

```On 09/18/2013 02:44 PM, Thieulot, C. (Cedric) wrote:
> here are the timings in optimised mode : still spending 30% of the time in the
> temperature assembly.
>
>
> 16536 +---------------------------------------------+------------+------------+
> 16537 | Total wallclock time elapsed since start    |  1.21e+04s |            |
> 16538 |                                             |            |            |
> 16539 | Section                         | no. calls |  wall time | % of total |
> 16540 +---------------------------------+-----------+------------+------------+
> 16541 | Assemble Stokes system          |      1801 |       355s |       2.9% |
> 16542 | Assemble temperature system     |      1801 |  3.66e+03s |        30% |
> 16543 | Build Stokes preconditioner     |         1 |      3.62s |      0.03% |
> 16544 | Build temperature preconditioner|      1801 |       514s |       4.3% |
> 16545 | Solve Stokes system             |      1801 |  5.83e+03s |        48% |
> 16546 | Solve temperature system        |      1801 |  1.16e+03s |       9.6% |
> 16547 | Initialization                  |         2 |     0.339s |    0.0028% |
> 16548 | Postprocessing                  |      1801 |       261s |       2.2% |
> 16549 | Setup dof systems               |         1 |      2.05s |     0.017% |
> 16550 +---------------------------------+-----------+------------+------------+

This is relatively typical. Assembling the temperature system is expensive,
because so many parts go into it (we need to evaluate the velocity, many
coefficients, and compute the artificial viscosity which involves the second
derivatives of the temperature field). We need to eventually look into whether
it is possible to cut corners somewhere. That said, if you have models with
spatially varying viscosity, or large processor counts -- in other words, the
interesting cases -- then the Stokes solver becomes significantly more
expensive and takes over much of the CPU time, so we've always felt that that
is the more critical piece...

Best
W.

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

```