Can't figure out where my mistake is?

Question

Aaron 2013-9-16

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/87295-can-t-figure-out-where-my-mistake-is

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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Answer 1

Walter Roberson 2013-9-16

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https://ww2.mathworks.cn/matlabcentral/answers/87295-can-t-figure-out-where-my-mistake-is#answer_96835

在 MATLAB Online 中打开

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 ?

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Aaron 2013-9-17

I've been trying to figure out where I messed up. I just can't find the error?

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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