nonzero m and d coefficients for Matlab PDE

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Siarhei Hladyshau
Siarhei Hladyshau 2019-3-17
评论： Joanna Chang 2020-8-6
Hello, everyone!
I am trying to solve the 2D problem with Matlab PDE and need to specify both mass (m) and damping (d) to be nonzero.
Workflow in short:
create model with
model = createpde(N);
specify geometry ...
coefficients:
specifyCoefficients(model, 'm', rho, 'd', d, 'c', c, 'a', 0, 'f', f);
and solve it:
result = solvepde(model,time);
I got stuck having the error:
Error using pde.CoefficientAssignment/checkMandD (line 303)
When both 'm' and 'd' coefficients are nonzeros, the 'd' coefficient must be a matrix.
In the documentation to the function "specifyCoefficients" it is said:
Note: If the PDE to solve has both 'm' and 'd' coefficients that are
non-zero, then 'd' must be a matrix that has the same size as
the discretized mass matrix (not to be confused with 'm').
What is the correct way to specify 'd' coefficient when mass is nonzero?

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采纳的回答

Ravi Kumar
Ravi Kumar 2019-3-19
Refer to this documentation:
https://www.mathworks.com/help/pde/ug/pde.pdemodel.specifycoefficients.html#bu7pwf5
d has to be a sparse matrix when m is non-zero.
  2 个评论
Joanna Chang
Joanna Chang 2020-8-6
I am following the instructions here but it is unclear how to create this sparse matrix. I have a PDE system with 2 equations and two variables u1 and u2, and d should be 0 in the first equation and 1 for u2 in the second equation, such that d=[0 0; 0 1], what should the matrix be if result.M is of size 120x120?

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