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Spectre DC Analysis Default for maxiters and maxsteps? (Read 1024 times)
lukeS
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Spectre DC Analysis Default for maxiters and maxsteps?
Aug 22nd, 2017, 6:42pm
 
1 - What are the default values for maxiters and maxsteps in the DC analysis convergence options for Spectre?

If I understand them correctly, maxiters is the maximum number of iterations of newton's method in solving for convergence. maxsteps is the maximum number of homotopic transformation steps in solving the problem.

2 - Will Spectre always take maxiters and maxsteps before reaching convergence? In other words, if the DC analysis does not converge, we are confident in saying the simulator has taken exactly maxiters steps in attempt to solve KCL using newton's method? Same idea for maxsteps...?

3 - Does the spectre simulator take a maximum of maxiters steps at each of the homotopic levels. For instance, doing 'source' homotopy, does the simulator take maxiters steps at each increment of the source voltages/currents? Can we say the simulator takes a maximum of maxiters*maxsteps calculation steps in solving the system? Or is this too naive to say..

Hope this makes sense, I appreciate any help!  :D
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Geoffrey_Coram
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Re: Spectre DC Analysis Default for maxiters and maxsteps?
Reply #1 - Aug 24th, 2017, 10:57am
 
lukeS wrote on Aug 22nd, 2017, 6:42pm:
2 - Will Spectre always take maxiters and maxsteps before reaching convergence? In other words, if the DC analysis does not converge, we are confident in saying the simulator has taken exactly maxiters steps in attempt to solve KCL using newton's method?


I don't know specifically for Spectre, but I believe that a Newton solver that encounters a math error will terminate on an earlier iteration and not do exactly maxiters.
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Andrew Beckett
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Re: Spectre DC Analysis Default for maxiters and maxsteps?
Reply #2 - Sep 9th, 2017, 12:23am
 
1. The default values can be seen from the output of "spectre -h dc".

2. I believe there are a number of reasons why the convergence algorithm would stop early - e.g. if it's clearly diverging - there will be points at which there is no point continuing. The precise details are something that are down to the implementation within the simulator (and are proprietary) and will have had many years of optimisation.

3. That's too naive.

I'm not sure why it matters to you?

Andrew.
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