MATLAB: Can you help me? Does anyone have a FEM code for Singular perturbation problems in 1D

femspp

Does anyone have a FEM for Differential equation epsilon u''+a(x)u'(x)+b(x)u(x)=f(x), u(a)=A, u(b)=B?

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Although the PDE Toolbox only currently supports 2D and 3D geometries, you should be able to "simulate" a 1D geometry by using a thin "pseudo" 2D rectangular geometry with no variation in the y-directions, and homogenous boundary conditions at the y-boundaries. Alternatively, the FEATool Multiphysics toolbox fully supports defining and solving custom 1D PDEs directly.

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MATLAB: Does robstab return stable perturbation

I agree that the values do not seem correct. In fact, strangely if you use the range [0.55, 1.5] with a nominal value of 1, then WCU will display the correct destabilizing value of tau (tau = 0). Furthermore, if you use a nominal value that is closer to the upper bound than the lower bound, then tau gets approximated to some value close to zero. I'm not sure why there is such an inconsistency in this function.

The issue seems to occur when the ureal parameter has an asymmetric range that is asymmetric past a certain degree, and occurs more often when the nominal value is closer to the lower bound than the upper bound.

I have notified the developers of this issue. Unfortunately, I suppose the only workaround for now is to use a symmetric range.

MATLAB: How to convert 3D matrix to 1D

The way to do this is to reshape your image into an nx3 matrix where each row correspond to the three colours of a pixel. You can then apply unique with the 'rows' option on this to get your labels. It's then just a matter of reshaping the output.

Note that doing the scanning by rows rather than by columns complicate the code somewhat.

Also, please, post valid matlab code rather than leaving it to us to generate valid matrix

A = cat(3, [22 22 39;89 23 99; 89 69 99],  ... it would have been great
           [10 10 40; 11 11 10; 11 10 10], ... if I could just have 
           [10 10 50; 14 11 10; 14 10 10]) %copy/pasted that from your question
[~, ~, labels] = unique(reshape(permute(A, [2 1 3]), [], 3), 'rows', 'stable');
B = reshape(labels, size(A, 2), size(A, 1))'

The same code if you do the labeling by column:

[~, ~, labels] = unique(reshape(A, [], 3), 'rows', 'stable'); %no need to transpose anymore
B = reshape(labels, size(A, 1), size(A, 2)) %no need to transpose either.

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Related Solutions

MATLAB: Does robstab return stable perturbation

MATLAB: How to convert 3D matrix to 1D

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