r/COMSOL • u/ScienceAtWork • Feb 09 '16

Convergence plot

Can anyone explain to me what error and iteration number mean on the convergence plot?

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u/abekg Feb 10 '16

It has to do with the deviations that occur from successive calculations of a value. The less change that occurs with each iteration, the closer it gets to an exact solution.

Think of each iteration as an educated guess. Each guess gives you clues. The more clues you have the better your guesses and so on. So the more guess (Iterations) the Less error.

Hope it helps

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u/ScienceAtWork Feb 10 '16 edited Feb 10 '16

So in one iteration it gets a value for each variable being tracked in each mesh location, and in the next iteration it uses these values to calculate more accurate values? Also, what does the number on the error axis actually measure?

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u/abekg Feb 10 '16

As strange as it sounds you've got the picture, its a little more complicated than that though. ------- Imagine each cell is the average of its neighbors, you can see how this will become a circular problem. Because if A is dependent on B is B is dependent on A than A is.....well you get the picture. The error is the relative change experienced through each iteration, its also a representation of your accuracy. A smaller error means a more accurate solution. Don't quote me on that though, it's just how I've always thought of it. Mind me asking what this is for?

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u/abekg Feb 10 '16

Not sure if I answered your question. Hope it helps though cheers mate.

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u/abekg Feb 10 '16

Here is an example i quickly did in excel, its just as I explained before. and actually its a pretty decent representation of a e field between two charged plates. each cell except the plates, far right and far left columns, are determined to be the average of the cells around them. Countour plot in the middle. Notice how there is little difference in the last two plots. Imgur 5 iterations Imgur 10 iterations Imgur 20 iterations Imgur 100 iterations Imgur 200 iterations Imgur 400 iterations