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Topic: measured boundary conditions with pde toolbox
Replies: 17   Last Post: Apr 8, 2014 6:00 AM

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Dmitry

Posts: 4
Registered: 4/2/14
Re: measured boundary conditions with pde toolbox
Posted: Apr 7, 2014 11:11 AM
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"Dmitry" wrote in message <lhipl8$f2q$1@newscl01ah.mathworks.com>...
> "Bill Greene" wrote in message <lhholl$pur$1@newscl01ah.mathworks.com>...
> > "Dmitry" wrote in message <lhhm8o$j16$1@newscl01ah.mathworks.com>...
> > > "Doug" wrote in message <h5psrj$8g9$1@fred.mathworks.com>...
> > > > OK, I've answered my own question, and the answer is a boundary M-file.
> > > >
> > > > Though wbound makes a boundary M-file that is based on a simple formula, in exactly the same format as a boundary condition matrix, it's possible to write your own boundary M-file *any way you like*. As long as it takes (p,e,u,time) as inputs and returns [q,g,h,r] as outputs, it works fine with assempde. You just pass the filename of the boundary M-file as the first argument to assempde. So I've written a boundary M-file that takes the necessary inputs (p,e,u,time) but ignores them, instead constructing [q,g,h,r] from my measurements. And it works. Reading the help file for pdebound over and over was the key!

> > >
> > > Hi Doug,
> > > Could you provide an example of this kind of usage please?
> > > As I understood, you just loaded the variable in the boundary M-file like this:

> > > > load('var.mat','var');
> > > and used it for construction of [q,g,h,r]. Am I right?
> > >
> > > I've done the same (for hyperbolic solver), but I can't check if it works because for some (another) reason the solver gives me the error:

> > > >Error using pdeexpd (line 57)
> > > >Number of variables mismatch between u and bl.
> > > >Error in assemb (line 101)
> > > > [q,g,h,r]=pdeexpd(p,e,u,time,bl);
> > > >Error in pdeODEInfo/getMats (line 164)
> > > > [Q,G,H,R]=assemb(self.b,self.p,self.e,u,time);
> > > >Error in pdeODEInfo/checkFuncDepen (line 60)
> > > > [MM0,K0,M0,F0,Q0,G0,H0,R0] = self.getMats(u0, t0);
> > > >Error in pdeHyperbolicInfo (line 15)
> > > > obj=obj.checkFuncDepen(u0, tlist);
> > > >Error in hyperbolic (line 41)
> > > > pdehyp=pdeHyperbolicInfo(u0,ut0,tlist,b,p,e,t,c,a,f,d);
> > > >Error in main (line 49)
> > > >u = hyperbolic(u0,ut0,tlist,b,p,e,t,c,a,f,d);

> > >
> > > In my case I have only dependence on time in boundary M-file, but the solver assumes that output of it depends on the solution u too
> > > (it goes wrong way at pdeODEInfo/checkFuncDepen stage).
> > > Don't know what to do...

> >
> > There appears to be something wrong with your pdebound function or
> > with how you are passing the handle to it into hyperbolic.
> >
> > Did you follow the example here if you have a single pde:
> >
> > http://www.mathworks.com/help/pde/ug/boundary-conditions-for-scalar-pde.html
> >
> > or here if you have a system of pde:
> >
> > http://www.mathworks.com/help/pde/ug/boundary-conditions-for-pde-systems.html
> >
> > Is the value of "b" that you are passing into hyperbolic something like this?
> >
> > b = @myPdeBoundFunction; % myPdeBoundFunction is whatever you named your function
> >
> > Bill

>
> Oh, thanks, Bill, I'd passed 'b' the wrong way...


Bill, could you help again please...
I have a time-dependent boundary conditions for hyperbolic solver, but when I displayed the variable time, which is passed in boundary.m, I saw it was nearly equal to 2*10^-15 during all calls. So hyperbolic() passes time=0 to BC-function all the time. Which it can be related to?



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