"Sashankh Rao" wrote in message <ki291f$56f$1@newscl01ah.mathworks.com>...
> I then mesh it: [p,e,t] = initmesh(g);
> Then I create my boundary matrix using [Q,G,H,R] = pdebound(p2,e2);
> I then assemble other matrices using [K,M,F] = assema(p,t,c,a,f);
> Finally I solve the problem using u = assempde(K,M,F,Q,G,H,R);
Ah, I see that the documentation page I pointed you to doesn't
show you what to do with the pdebound function once you've created it--
sorry.
That function is actually called by the PDE Toolbox routines-- not by you.
If you don't want to do anything fancy, but simply want a solution, do this:
b=@pdebound; % the "pdebound" function can have any name
% also define p,e,t,c,a,f
u=assempde(b,p,e,t,c,a,f);
Regards,
Bill
> ------------------------------------------
> As per the link below the size of the Q matrix in the boundary file is (N^2 ne) which for a one-dimensional system is (1 ne), where ne is the number of edges in the mesh.
>
> http://www.mathworks.com/help/pde/ug/boundary-conditions-for-scalar-pde.html
>
> However the size for the K and M matrices is (Np Np) where Np is the number of nodes in the matrix.
>
> So I see that the K matrix and Q matrix are not of the same dimensions and hence the error. I am not able to figure out how to fix this problem. Any help will be appreciated very much.
>
> Thank you.
>
> "Bill Greene" wrote in message <khfgev$sgb$1@newscl01ah.mathworks.com>...
> > Hi,
> >
> > "Sashankh Rao" wrote in message <khdu9o$j3c$1@newscl01ah.mathworks.com>...
> > > Using the Matlab pde toolbox I obtain a solution to the Poisson equation for a given geometry using dirichlet boundary conditions. First, I want to determine the gradient at all the boundary nodes. Is this possible using the toolbox? Second, I want to use these gradient values as an input boundary condition for the same boundary to solve a different equation (same geometry). Is this possible to do using the toolbox? Thanks.
> >
> > Yes, this is definitely possible. I'll try to point you in the right direction.
> >
> > The function pdegrad can be used to calculate the gradient of the solution at the
> > element centroids.
> > http://www.mathworks.com/help/pde/ug/pdegrad.html?searchHighlight=pdegrad
> > Then the function pdeprtni can be used to interpolate these centroid values back
> > to the nodes.
> > http://www.mathworks.com/help/pde/ug/pdeprtni.html
> >
> > Using these gradient values in the boundary conditions will require you to write your
> > own boundary condition function, referred to as a "boundary file" in the PDE
> > Toolbox documentation.
> > http://www.mathworks.com/help/pde/ug/pdebound.html
> >
> > This documentation page has some examples of how to write such a function.
> > http://www.mathworks.com/help/pde/ug/boundary-conditions-for-scalar-pde.html
> >
> > Bill![]()
> I then mesh it: [p,e,t] = initmesh(g);
> Then I create my boundary matrix using [Q,G,H,R] = pdebound(p2,e2);
> I then assemble other matrices using [K,M,F] = assema(p,t,c,a,f);
> Finally I solve the problem using u = assempde(K,M,F,Q,G,H,R);
Ah, I see that the documentation page I pointed you to doesn't
show you what to do with the pdebound function once you've created it--
sorry.
That function is actually called by the PDE Toolbox routines-- not by you.
If you don't want to do anything fancy, but simply want a solution, do this:
b=@pdebound; % the "pdebound" function can have any name
% also define p,e,t,c,a,f
u=assempde(b,p,e,t,c,a,f);
Regards,
Bill
> ------------------------------------------
> As per the link below the size of the Q matrix in the boundary file is (N^2 ne) which for a one-dimensional system is (1 ne), where ne is the number of edges in the mesh.
>
> http://www.mathworks.com/help/pde/ug/boundary-conditions-for-scalar-pde.html
>
> However the size for the K and M matrices is (Np Np) where Np is the number of nodes in the matrix.
>
> So I see that the K matrix and Q matrix are not of the same dimensions and hence the error. I am not able to figure out how to fix this problem. Any help will be appreciated very much.
>
> Thank you.
>
> "Bill Greene" wrote in message <khfgev$sgb$1@newscl01ah.mathworks.com>...
> > Hi,
> >
> > "Sashankh Rao" wrote in message <khdu9o$j3c$1@newscl01ah.mathworks.com>...
> > > Using the Matlab pde toolbox I obtain a solution to the Poisson equation for a given geometry using dirichlet boundary conditions. First, I want to determine the gradient at all the boundary nodes. Is this possible using the toolbox? Second, I want to use these gradient values as an input boundary condition for the same boundary to solve a different equation (same geometry). Is this possible to do using the toolbox? Thanks.
> >
> > Yes, this is definitely possible. I'll try to point you in the right direction.
> >
> > The function pdegrad can be used to calculate the gradient of the solution at the
> > element centroids.
> > http://www.mathworks.com/help/pde/ug/pdegrad.html?searchHighlight=pdegrad
> > Then the function pdeprtni can be used to interpolate these centroid values back
> > to the nodes.
> > http://www.mathworks.com/help/pde/ug/pdeprtni.html
> >
> > Using these gradient values in the boundary conditions will require you to write your
> > own boundary condition function, referred to as a "boundary file" in the PDE
> > Toolbox documentation.
> > http://www.mathworks.com/help/pde/ug/pdebound.html
> >
> > This documentation page has some examples of how to write such a function.
> > http://www.mathworks.com/help/pde/ug/boundary-conditions-for-scalar-pde.html
> >
> > Bill