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weird behavior in data after extracting it from COMSOL plot with LiveLink

Posted Oct 9, 2023, 6:31 p.m. EDT LiveLink for MATLAB, Results & Visualization, Structural Mechanics Version 6.1 3 Replies

Helge Schaab
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Hello there,

When extracting the data points of a line plot from COMSOL with something like: data = mphplot(model,'pg37'); y_data_plot = data{1,1}{1,1}.d; I get this weird 'noise' in my data which can be seen in the Matlab plot. The attached pictures show the problem. This is a problem for my post processing as I need to determine the local maxima/minima. It seems like a numerical issue but I don't know how. Has someone seen this behavior before?

To give some background, I perform a contact study where a structure is pushed against a counter surface. The plots show the distance between the deformed configuration of the bottom domain of the structure and the counter surface.

3 Replies Last Post Oct 11, 2023, 2:49 a.m. EDT
Lars Gregersen COMSOL Employee

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Posted: 7 months ago Oct 10, 2023, 5:00 a.m. EDT

Hi Helge

Depending on where Comsol gets its data from the order of the data may depend on the mesh and other settings.

The field data{1}{1}.t tells you the order of the data. I.e. the t-field contains two numbers (start-index end-index) for each line segment in the plot.

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Lars Gregersen
Comsol Denmark
Hi Helge Depending on where Comsol gets its data from the order of the data may depend on the mesh and other settings. The field data{1}{1}.t tells you the order of the data. I.e. the t-field contains two numbers (start-index end-index) for each line segment in the plot.
Helge Schaab
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Posted: 7 months ago Oct 10, 2023, 9:14 a.m. EDT

Hi Lars,

thank you for the hint! I couldn't figure out how to plot it correctly with the simplex indices so below a workaround/solution which is easy and worked for me (for anyone encountering this in the future):

you can get the correct order of the y-data in Matlab by first sorting the x-data with: [x-data_sorted,order-x] = sort(x-data); and then sorting the y-data according to the order of the x-data with: y-data_sorted = y-data(order-x);

greetings, Helge

Hi Lars, thank you for the hint! I couldn't figure out how to plot it correctly with the simplex indices so below a workaround/solution which is easy and worked for me (for anyone encountering this in the future): you can get the correct order of the y-data in Matlab by first sorting the x-data with: \[x-data\_sorted,order-x\] = sort(x-data); and then sorting the y-data according to the order of the x-data with: y-data\_sorted = y-data(order-x); greetings, Helge
Lars Gregersen COMSOL Employee

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Posted: 7 months ago Oct 11, 2023, 2:49 a.m. EDT

Hi Helge

Plotting is easy. Just do (for lines): patch('vertices', pd{1}{1}.p', 'faces', pd{1}{1}.t'+1)

You can of course also just do this: mphplot(pd) ;-)

If you know that your data has increasing x-valees (or y-values) then you can sort the data and perform the plotting or data analysis on the sorted data. Not all data are like that. Data may have gaps and/or have x- and y-values that can't be sorted in to an increasing sequence. This is the reason mphplot return the data in the form that it does.

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Lars Gregersen
Comsol Denmark
Hi Helge Plotting is easy. Just do (for lines): patch('vertices', pd{1}{1}.p', 'faces', pd{1}{1}.t'+1) You can of course also just do this: mphplot(pd) ;-) If you know that your data has increasing x-valees (or y-values) then you can sort the data and perform the plotting or data analysis on the sorted data. Not all data are like that. Data may have gaps and/or have x- and y-values that can't be sorted in to an increasing sequence. This is the reason mphplot return the data in the form that it does.

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