# Help for setting varying timesteps

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 September 10, 2009, 04:46 Help for setting varying timesteps #1 New Member   Andrej Hoyningen Join Date: Jul 2009 Posts: 22 Rep Power: 9 The simple solution is always hard to get. After having searched in the forum for a good solution to set varying timesteps with an CEL expression without sucess, here is my way to obtain: first 300 iterations -> 0.7s next 300 iterations -> 0.01s CEL Expression: 0.7[s]-0.69*step(citern-301)[s] I hope I can help somebody who has the same task. andrej

 September 10, 2009, 06:32 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 You could also have done it with a 1D interpolation function. Same end effect, but possibly easier to understand.

 September 11, 2009, 05:08 #3 New Member   Andrej Hoyningen Join Date: Jul 2009 Posts: 22 Rep Power: 9 I wanted to change the time in a jump function. But is a linear change better in regard to convergence?

 September 11, 2009, 07:32 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 You can define step functions in the 1D interpolation function. The following series of points define a step function good enough for most people: (0,0), (0.999999999999,0), (1,1), (2,1) Yes, a sudden change in time step size can cause convergence issues. It will cause accuracy issues as well. Ramping the time step change will help both problems.

 Tags cel expression, time, timestep, varying timesteps

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