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Possible Inconsistency Between mpheval and mphmatrix?

Posted May 11, 2011, 8:23 p.m. EDT Interfacing Version 4.1 1 Reply

Brian McBee
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Using livelink with MATLAB, I am trying to get a handle on how the various state matrices/vectors are handled. Right now I'm confused by what seems to be a discrepancy using the attached extremely simple heat transfer model. In Matlab, I enter the following lines:

>> model = mphload('mcbee15.mph');
>> dat=mpheval(model, {'x' 'y' 'T'});
>> solution=mphgetu(model);

I then compare the node 'x' value (col 1), the node 'y' value (col 2), and the node 'T' value (col 3) as given to me by the mpheval command. Column 4 is the output of 'T' from the mphgetu command. I expected columns 3 and 4 to match up perfectly, but they are completely different permutations of the same 'T' values.

>> [dat.d1',dat.d2',dat.d3',solution]

ans =

0.7500 0 1.0000 1.0000
1.0000 0 1.0000 0.8621
0.7500 0.2500 0.8621 0.7453
1.0000 0.2500 0.8621 0.6672
0.7500 0.5000 0.7453 0.6398
1.0000 0.5000 0.7453 1.0000
0.7500 0.7500 0.6672 1.0000
1.0000 0.7500 0.6672 1.0000
0.7500 1.0000 0.6398 1.0000
1.0000 1.0000 0.6398 0.8621
0.5000 0 1.0000 0.7453
0.5000 0.2500 0.8621 0.6672
0.2500 0 1.0000 0.6398
0.2500 0.2500 0.8621 0.8621
0 0 1.0000 0.8621
0 0.2500 0.8621 0.8621
0.5000 0.7500 0.6672 0.7453
0.5000 1.0000 0.6398 0.6672
0 0.5000 0.7453 0.6398
0.2500 0.5000 0.7453 0.7453
0.2500 0.7500 0.6672 0.7453
0.2500 1.0000 0.6398 0.6672
0 0.7500 0.6672 0.6398
0 1.0000 0.6398 0.6672
0.5000 0.5000 0.7453 0.6398


Can anyone please explain the discrepancy? Also, which one of these would represent the coefficient vector that would be pre multiplied by the non-reduced stiffness matrix? Does dat.p truely give me the x,y coordinates of each node or am I missing something?

Thanks much!

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1 Reply Last Post Nov 1, 2011, 5:17 a.m. EDT
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Hello Brian McBee

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Laurin Wissmeier
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Posted: 1 decade ago Nov 1, 2011, 5:17 a.m. EDT
I have noted the same difference. You can get the coordinates of the solution vector that is retrieved by mphgetu using

xmi = mphxmeshinfo(model);
solCoords = xmi.dofs.coords;

The node index retrieved by
nodeNum = xmi.dofs.nodes;
indicates that the nodes are not sorted.

If you want to get derived variables in the same node order as the solution vector you need to use mphinterp at the coordinates of the respective nodes.

[~,loc] = unique(nodeNum);
out_COMSOL.theta = mphinterp(model,'dl.theta',...
'coord',solCoords(:,loc))';

At least, that's how I do it...
If there is a more elegant way, please let me know.
I have noted the same difference. You can get the coordinates of the solution vector that is retrieved by mphgetu using xmi = mphxmeshinfo(model); solCoords = xmi.dofs.coords; The node index retrieved by nodeNum = xmi.dofs.nodes; indicates that the nodes are not sorted. If you want to get derived variables in the same node order as the solution vector you need to use mphinterp at the coordinates of the respective nodes. [~,loc] = unique(nodeNum); out_COMSOL.theta = mphinterp(model,'dl.theta',... 'coord',solCoords(:,loc))'; At least, that's how I do it... If there is a more elegant way, please let me know.

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