solvepde fails on complex 'f' coefficient
5 views (last 30 days)
Show older comments
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!
0 Comments
Answers (2)
Ravi Kumar
on 26 Jun 2018
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 Comments
Hansu zhang
on 17 Mar 2019
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
Alan Weiss
on 21 Jul 2016
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 Comments
Yauhen
on 26 Jun 2018
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
See Also
Categories
Find more on Boundary Conditions in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!