With the size of the model (see below), I was not surprised at the long solve time. However, I did not understand the message "Linear solver failed. Reverting to build-in solver".

Here are the solver settings. I did not intentionally change from default. Perhaps I should have :-) I note there are several solvers to choose from. Which one is built-in?

Also, I note that the initial conditions specify "Expression" rather than "Computed solution". Was this my mistake?

I have included the Command log and the model Matlab and script files.

-Randal

======== begin Command Log ========

Grid Statistics:

Grid Generation Done.

number of grid points: 171780

number of grid cells: 981743

grid cell min volume: 0.0012

grid cell mean volume: 0.0081

grid cell max volume: 0.0238

grid cell min quality: 0.2459

grid cell mean quality: 0.7938

number of boundaries: 14

number of subdomains: 2

time for grid generation: 256.8838

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Solver Statistics (solvestat)

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Number of dependent variables

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V : 171780

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Simulation timings

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t_asm(A) : 3.1s \ 0%

t_asm(f) : 0.0s \ 0%

t_sparse : 6.6s \ 0%

t_bdr : 1.9s \ 0%

t_lc/mv : 0.0s \ 0%

t_solve : 2424.4s \ 97%

t_tot : 2489.2

--------------------------------------------------

[Warning: Linear solver failed. Reverting to built-in solver.]

======== end Command Log =========

box20x20x20m&sphere1m-solved.fesbox20x20x20m&sphere1m-solved.m