output history and testing convergence

Hi there,

I have quite a complicated algorithm running and I would like to test to see if it converges as it is taking a very long time to run. How do I go about using my output from my while loops on each iteration, putting them into a graph so I can see if they converge??

Answer 1

[Matt J]

 x=nan(1,MaxIterations);

 while i<=MaxIterations

   ...

   x(i)=...

   plot(x), drawnow

   i=i+1

 end

However, it's debatable whether this can give you true information about convergence, if you don't know what x(i) is converging to.

[Bran]

ank you! I will try this now. To be honestwhat the answer converges too is not really important, instead I need to see that the values between iterations are converging as my loop will stop once the matrices between consecutive iterations fail to differ by more than 0.1%

[Bran]

Oh unfortunately my information is 3D and so plot wont work!

[Matt J]

instead I need to see that the values between iterations are converging as my loop will stop once the matrices between consecutive iterations fail to differ by more than 0.1%

OK, so as an example, the sequence log(i), i=1,..., will show decreasing percent differences between log(i) and log(i+1) that eventually converge to zero. But you don't care that log(i) ---> inf ?

Oh unfortunately my information is 3D and so plot wont work!

Consider PLOT3, SCATTER3, or any of the various 3D plotting commands.