# Explicit converging faster compared to implicit

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 January 20, 2012, 05:43 Explicit converging faster compared to implicit #1 New Member   C.Harish Join Date: Jun 2011 Posts: 15 Rep Power: 7 Hello, can anyone tell me are there any cases where the explicit scheme converges faster compared to implicit, if so why does that happen?

 January 20, 2012, 18:16 #2 Senior Member   cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 12 If the physical timestep is very small, i.e. close to the explicit time step, explicit schemes will be faster.

 January 21, 2012, 05:14 #3 New Member   C.Harish Join Date: Jun 2011 Posts: 15 Rep Power: 7 Thanh for d reply cfdnewbie. Can u just eloborate it a bit more...also some of d example cases if u can...

 January 21, 2012, 11:58 #4 Senior Member   cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 12 it totally depends on your physics, your implementation and your hardware. It is not clear-cut, so there's no classical example. The smaller the timescales governing the flow, the larger your available number of cpus, the likelier the explicit scheme is to outperform the implicit one.

January 22, 2012, 17:57
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Quote:
 Originally Posted by harish_0689@ Hello, can anyone tell me are there any cases where the explicit scheme converges faster compared to implicit, if so why does that happen?
Depends on what you mean with converge. Do you mean "convergence to steady state" or do you mean "convergence in the linear solver" or something else?

Explicit schemes are faster at each time-step since they do not need to solve a system of equations.

However, implicit schemes can take much larger time-steps. If you have implicit treatment of the non-linear terms then you also need some way to deal with this.

So basically:

Quote:
 Originally Posted by cfdnewbie If the physical timestep is very small, i.e. close to the explicit time step, explicit schemes will be faster.
Cheers!
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 January 23, 2012, 08:00 #6 New Member   C.Harish Join Date: Jun 2011 Posts: 15 Rep Power: 7 i mean its convergence to the steady state.

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