Discussion Forum

Hello everyone,

For parametric sweep, I don't want to setup my relative tolerance to be a large number to start with, but sometimes when it is small enough it does make my solver to yell at me saying it does not converge.

So here is the story, a parametric sweep of variable Vg=1,2,3,4,5...to 10
Normally I setup my relative tolerance to be 1e-7, and it worked OK until the parametric sweep reached 4.4, for example. Then COMSOL stopped, saying that the relative tolerance is too small that it could not find a solution. But the SolEst are all OK it is the LinErr is large. Sometimes it would still say it could not find solution even though SolEst reaches 1e-10, this is weird. It just would not stop.

I am hoping someone can point me to the right direction on how to stop the simulation and save the solution when it diverges. If the computation screwed up at V=5, it is fine, just save the solution for V=1 through 4. And I will setup another study step for 5 through 10 using another tolerance.

The capture image shows how I setup my study: For each study step there are four nodes:
1. Compile Equations
2. Dependent Variable
3. Stationary Solver
4. Store Solutions
And each study step corresponds to a parametric sweep. The last sweep I am running the voltage sweep from 4V to 4.5V and the computation screwed up at 4.4 V

Now all the solutions can be used between 4V to 4.3V, except they are stored in "Study2/Vg sweep solver" node, not in "Study2/Vg 4V-4.5V" node. The first one I can do post processing but because it is a dynamic solution node, I can't use the 4.3V solution as the initial condition to solve for further parametric sweep after 4.5V. It would overwrite this solution node and, everything will be screwed.

I am wondering:
1. whether COMSOL has a function to save my solution from 4V to 4.3V, even it cannot find a convergence answer for 4.4V and further?
2. how to terminate a simulation? why the SolEst is much much smaller than my relative tolerance and the computation still goes on? And also it decreased the damping factor along the way?

I would much appreciate any suggestions or answers!!