solvepde fails on complex 'f' coefficient

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Avraham Klein
Avraham Klein 2016-7-20
评论： Hansu zhang 2019-3-17
I am trying to solve a pde using complex coefficients. However I am running into the following issue. Whenever I run solvepde I get an error regarding the complex coefficients.
Here is a MWE:
model = createpde();
geometryFromEdges(model, @circleg);
applyBoundaryCondition(model, 'Edge', 1:model.Geometry.NumEdges, 'u', 0);
generateMesh(model);
fC = @(r, s) complex(1i*ones(1,numel(r.x)));
specifyCoefficients(model, 'm', 0, 'd', 0, 'a', 0, 'c', 1, 'f', fC);
solvepde(model)
Which gives me:
Error using formGlobalKF2D Coefficient evaluation function, "@(r,s)complex(1i*ones(1,numel(r.x)))", returned a complex matrix but previously returned a real matrix. This function must consistently return the same type of matrix.
Any help would be very welcome! Thank you!

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回答（2 个）

Ravi Kumar
Ravi Kumar 2018-6-26
Hi Yauhen,
The expression
exp((r.x.^2+r.y.^2)/2).*exp(-1i.*s.time)
evaluates to real 1 when s.time =0, r.x= 0, r.y=0. Solver detects switching from real to complex or vice versa. To ensure the value of fC is consistent, please use the following expression for fC.
fC = @(r, s) complex(exp((r.x.^2+r.y.^2)/2).*exp(-1i.*s.time));
In this case fC = 1+0i when s.time =0, r.x= 0, r.y=0. Thus keeping it consistent throughout the solution.
Regards,
Ravi
  2 个评论
Yauhen
Yauhen 2018-6-26
Finally it works!
Thank you very much.
Yauhen
Hansu zhang
Hansu zhang 2019-3-17
Thank you Ravi Kumar
My matlab error "returned a complex matrix but previously returned a real matrix. This function must consistently ret". Your expression for fC works well . (ง •̀_•́)ง

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Alan Weiss
Alan Weiss 2016-7-21
It seems to me that your problem would be best solved by setting the f coefficient to 1i, a constant rather than a function. However, when I tried that, it did not work in solvepde. It is possible that there is a bug in solvepde; the development team is investigating.
Meanwhile, you might do better to use the legacy workflow using assempde.
Sorry, that is all I have at the moment.
Alan Weiss
MATLAB mathematical toolbox documentation
  8 个评论
显示 6更早的评论
Yauhen
Yauhen 2018-6-26
Hi Ravi Kumar, Thank you for fast reply, here is an example of the code:
model = createpde();
geometryFromEdges(model, @circleg);
applyBoundaryCondition(model, 'Edge', 1:model.Geometry.NumEdges, 'u', 0);
generateMesh(model,'Hmax',0.1);
fC = @(r, s) exp((r.x.^2+r.y.^2)/2).*exp(-1i.*s.time);
dC = -1i;
specifyCoefficients(model, 'm', 0, 'd',dC, 'a', 0, 'c', 1, 'f', fC);
setInitialConditions(model,0);
nframes = 30;
tlist = linspace(0,0.1,nframes);
result = solvepde(model,tlist)
u = result.NodalSolution;
The errors are:
Error using formGlobalKF2D
Coefficient evaluation function, "@(r,s)exp((r.x.^2+r.y.^2)/2).*exp(-1i.*s.time)", returned a complex matrix
but previously returned a real matrix. This function must consistently return the same type of matrix.
Error in pde.DiscretizedPDEModel/getStationaryFEMatrices (line 80)
[K, F] = formGlobalKF2D(self.emptyPDEModel, self.p, self.t, self.coefstruct,u,time);
Error in pde.DynamicDiscretizedPDEModel/getDynamicFEMatrices (line 118)
[K,A,F,Q,G,H,R] = self.getStationaryFEMatrices(u,time);
Error in pde.DynamicDiscretizedPDEModel/checkSpatialCoefsForUorTDependence (line 52)
[Mass0,K0,A0,F0,Q0,G0,H0,R0] = self.getDynamicFEMatrices(u0, t0);
Error in pde.DynamicDiscretizedPDEModel (line 38)
obj = obj.checkSpatialCoefsForUorTDependence(u0,tlist);
Error in pde.EquationModel/solveTimeDependent (line 25)
femodel=pde.DynamicDiscretizedPDEModel(self,p,e,t,coefstruct,u0,tlist,tsecondOrder);
Error in pde.PDEModel/solvepde (line 54)
[u,dudt] = self.solveTimeDependent(coefstruct, u0, ut0, tlist, ...
Do you have any ideas what is wrong here?
Best regards
Ravi Kumar
Ravi Kumar 2018-6-26
I posted an answer that fixes the error.

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