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nvsuryan1-Visitor
1-Visitor
Jul 26, 2014 12:25 AM UTC
Question

Numwrical integration

I numerically integrated a non-linear two-point boundary layer problem using Mathcad 11 and Mathcad 15. The two give slightly different values with Mathcad 11 producing a more plausible result. Anyone knows the reason for the difference?

9 replies

AlanStevens19-Tanzanite
19-Tanzanite
Jul 26, 2014 6:23 AM UTC

Can't tell without seeing the worksheets. Upload them.

Alan

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nvsuryan1-VisitorAuthor
1-Visitor
Aug 7, 2014 1:26 AM UTC

The attached file shows the actual programming

As I said before the difference is small but it bothered me that the same software should give slightly different results.

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PhilipOakley1-Visitor
1-Visitor
Jul 26, 2014 8:26 PM UTC

As I remember it the default integration method has changed between V11 and V15, so slight variation can come from that.

In addition it is easily possible to badly formulate the equation being integrated, such that the algorithm doesn't find (when searching for high points in the graph) the area under the curve - this is particularly true for graphs that are shown on a log-log scale in text books, which are simply a spike on a lin-lin plot (i.e. as seen by the numeric integral). I'd expect PDE/ODEs to have a problem with this some times.

As said by Alan, at least post an example sheet that extracts the issue you are demonstrating.

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nvsuryan1-VisitorAuthor
1-Visitor
Aug 1, 2014 2:12 AM UTC

I again compared the results of numerical intgration in thwo versions with identical boundary conditions. Thre is a slight difference in the results, which, I think are caused by the default items in the two versions.

But the differences are small and not worth pursuing any further.

Thanks for helping me out.

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MikeArmstrong1-Visitor
1-Visitor
Aug 1, 2014 6:41 AM UTC

Again no example. This thread is pointless without examples to work with.

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