Can't figure out where my mistake is?

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Aaron
Aaron 2013-9-16
Trying to solve boundary value problem. I have a template to work off of but I'm not sure where I am coding wrong.
function bvp4c_prob4hw3
global L epsf epsi R T F Cint Z
%
% assign values to constants
%
L = (50*10^-9);
epsf = 80;
epsi = (8.854*10^-12);
R = 8.314;
T = 298;
F = 96490;
Cint = 10;
Z = -0.05;
%
%
xlow=Z;
xhigh=L;
solinit=bvpinit(linspace(Z,L,20),[Z 0]);
sol=bvp4c(@bvpode,@bvpbc,solinit);
plot(sol.x,sol.p(2,:),'b--');
%
%
function dydx=bvpode(x,p)
global L epsf epsi R T F Cint Z
dydx=[p(2) -(F*Cint/epsf*epsi)*(exp(-F*p(1)/R*T) - exp(F*p(1)/R*T))];
%
%
function res=bvpbc(ya,yb)
global L epsf epsi R T F Cint Z
res=[ya(1)-Z yb(1)-L];
This is the error I get:
Error using bvp4c (line 252)
Unable to solve the collocation equations -- a singular Jacobian encountered.
Error in bvp4c_prob4hw3 (line 19)
Line 252? There aren't enough lines?

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回答（1 个）

Walter Roberson
Walter Roberson 2013-9-16
Your dydx calculation is generating NaN or infinity for at least one of the entries.
At the command prompt, give the command
dbstop if infnan
and run; it should stop when it has encountered the problem. Then try to figure out why it happened. For example could p entries become large and negative ?
  2 个评论
Aaron
Aaron 2013-9-17
I've been trying to figure out where I messed up. I just can't find the error?
Walter Roberson
Walter Roberson 2013-9-17
Has the dbstop worked?
Have you tried standard debugging such as adding in a counter that prints out, so you can tell how many iterations until failure? And then putting in a breakpoint that keys on that counter, then step through looking at the arguments?

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