What is wrong about my "specifyCoefficients" function use for PDEModel?

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Jan Schäppi
Jan Schäppi 2018-11-29
评论： Jan Schäppi 2018-11-29
I am trying to solve the Schnakenberg Model, a (nonlinear) PDE system in 2D:
=
=
My code by now is the following:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Define Model
nEquations = 2;
model = createpde(nEquations);
%% Define Geometry
geometryFromEdges(model,@lshapeg);
%% Define Schnakenberg Model Nonlinear Function
a = 1; b = 0.5; gamma = 200; d = 20;
R = @(c) gamma*[a - c(1)+c(1)*c(2)*c(2);
b - c(1)*c(2)*c(2)];
D = [1 0; 0 d];
%% Solve Problem on Model
m_mod = zeros(2); d_mod = eye(2); a_mod = zeros(2);
c_mod = [D(1,1) 0 0 0;
0 0 0 0;
0 0 0 0;
0 0 0 D(2,2)];
f_mod = @(location,state) R(state.u);
specifyCoefficients(model,'m',m_mod,'d',d_mod,'c',c_mod,'a',a_mod,'f',f_mod);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
However as an output I get the following:
Error using pde.CoefficientAssignment/checkMCoefSize (line 398)
Size of the matrix 'm' is not consistent with
the pde.PDEModel/PDESystemSize property.
Error in pde.CoefficientAssignment/checkAllMatrixCoefSizes (line 240)
self.checkMCoefSize(self.m, systemsize);
Error in pde.CoefficientAssignment (line 103)
obj.checkAllMatrixCoefSizes(systemsize, numdims);
Error in pde.PDEModel/specifyCoefficients (line 139)
coef = pde.CoefficientAssignment(coefcont,argsToPass{:});
Error in ForumAttempt (line 21)
specifyCoefficients(model,'m',m_mod,'d',d_mod,'c',c_mod,'a',a_mod,'f',f_mod);
Where did I go wrong? I think I followed the Instructions at https://ch.mathworks.com/help/pde/ug/equations-you-can-solve.html
where it states "For systems of N equations, the coefficients m, d, and a are N-by-N matrices, f is an N-by-1 vector, and c is a 2N-by-2N tensor (2-D geometry)"

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采纳的回答

Ravi Kumar
Ravi Kumar 2018-11-29
Can you try using:
specifyCoefficients(model,'m',0,'d',d_mod,'c',c_mod,'a',0,'f',f_mod);
and see if you get the solution?
Regards,
Ravi
  5 个评论
显示 3更早的评论
Ravi Kumar
Ravi Kumar 2018-11-29
Sorry didn't notice this earler.This shold be the final one.
specifyCoefficients(model,'m',0,'d',d_mod(:),'c',c_mod(:),'a',0,'f',f_mod);
Refer to the documentation of c-coefficient for example:
"To write the coefficient c for inclusion in the PDE model via specifyCoefficients, give c as either of the following:
  • If c is constant, give a column vector representing the elements in the tensor.
  • If c is not constant, give a function handle. The function must be of the form"
You need to arrage c-coefficient correctly so that c_mod(:) represent the correct tensor.
Jan Schäppi
Jan Schäppi 2018-11-29
This has solved my problem, I would never have come up with it myself. Thank you so much for your help!

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