MATLAB: Evaluating gradient of eigenvectors.

eigenvalue problempde toolbox

Suppose I use Matlab's pde toolbox to solve an eigenvalue problem using FEM. Specifically I am using:

result=solvepdeeig(model,[0,10]);
eigenvectors = result.Eigenvectors;
eigenvalues = result.Eigenvalues;

Is there a way of evaluating the gradient of the computed eigenvectors, say using something similar to the

evaluateGradient

function?

Best Answer

Hi Matt,

The values in eigenvectors are scaled values, with no option to re-scale them or normalize as per choice. Hence, they do not have a physical meaning. So evaluating gradients using them is not suggested.

Can you explain why do you need to take gradients of eigenvectors? I could suggest a workaround depending on your use case.

Regards, Ravi

Related Solutions

MATLAB: Solving eigenvalues PDE problem

Hi Haya,

You need to setup the problem using new workflow:

model = createdpde;

Then assign the geometry to the model using decsg and geometryFromEdges functions, first export the geomery using the option in Draw menu of pdetool and then execute the following commands:

g = decsg(gd,sf,ns)

geometryFromEdge(model,g);

The fillin the rest of the details of the model using specifyCoefficient and applyBoundaryConditions function, check for the documentation on the syntax.

Once you are done defining the model, you can generate the mesh and solve for eigenvalue as:

generateMesh(model)

Reign = solvepdeeig(model,[-100, upperFreqLimit])

Regards,

Ravi

MATLAB: It’s possible to update nodes value in a mesh that was created with pde toolbox

Hello Gabriel,

You can achieve this using geometryFromMesh function. Following your example:

results = solvepde(model);
u = results.NodalSolutions;
oldNodes = model.Mesh.Nodes;
newNodes = oldNodes + u';
elements = model.Mesh.Elements;
% Delete the geometry. As you will create new geometry with deformed mesh.
model.Geometry = []
newMesh = geometryFromMesh(model,newNodes,elements);