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Coupled Mass and energy equations using bvp4c
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Jagadeesh Korukonda
am 12 Dez. 2021
Kommentiert: Star Strider
am 12 Dez. 2021
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/832085/image.png)
clc,clear,close
global Pem Peh Da b U yw yf
Pem = 2000; Peh = 500;
Da = 1e8; b = 0.015;
U = 1; yw = 0.9; yf = 0.0503;
z = linspace(0,1);
%guess = 4*ones(1,2);
solinit = bvpinit(z,[1,0,1,0]);
sol = bvp4c(@myfun,@mybc,solinit);
function F = myfun(~,y)
global Pem Peh Da b U yw
y1 = y(1);
y2 = y(2);
y3 = y(3);
y4 = y(4);
F(1) = y2;
F(2) = Peh*(y2 + b*Da*y3*exp(-1/y1) - U*(yw-y1));
F(3) = y4;
F(4) = Pem*(y4 + Da*y3*exp(-1/y1));
F = F(:);
end
function f = mybc(ya,yb)
global Pem Peh yf
f(1) = ya(2)+Peh*(yf-ya(1));
f(2) = yb(2);
f(3) = ya(4) + Pem*(1-ya(3));
f(4) = yb(4);
f=f(:);
end
function g = guess(z) % initial guess for y and y'
g = [0.5
0.5
0.5
0.5];
end
I wrote code like this but I'm getting error as
Error using bvp4c (line 248)
Unable to solve the collocation equations -- a singular Jacobian encountered.
Error in Q2 (line 11)
sol = bvp4c(@myfun,@mybc,solinit)
can someone help in this regard
thanks in advance
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Akzeptierte Antwort
Star Strider
am 12 Dez. 2021
Ths usual solution for that is to simply increase the initial mesh size, and here that is:
z = linspace(0,1,7500);
It then runs without error. (I used yyaxis because
is more than an order of magnitude greater than the others, and those details get lost plotting them on the same axes.)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/832125/image.png)
Also, please never use global variables! Pass them as extra parameters, as I did here.
Increasing the size of ‘z’, correcting the global variable problem, and plotting with yyaxis are the only changes I made to the posted code.
% global Pem Peh Da b U yw yf
Pem = 2000; Peh = 500;
Da = 1e8; b = 0.015;
U = 1; yw = 0.9; yf = 0.0503;
z = linspace(0,1,7500);
%guess = 4*ones(1,2);
solinit = bvpinit(z,[1,0,1,0]);
sol = bvp4c(@(t,y)myfun(t, y, Pem,Peh, Da, b, U, yw, yf),@(ya,yb)mybc(ya,yb, Pem, Peh, yf),solinit)
figure
yyaxis left
plot(sol.x, sol.y(1:3,:))
yyaxis right
plot(sol.x, sol.y(4,:))
grid
legend(compose('y_%d',1:size(sol.y,1)), 'Location','S')
function F = myfun(t, y, Pem,Peh, Da, b, U, yw, yf)
% global Pem Peh Da b U yw
y1 = y(1);
y2 = y(2);
y3 = y(3);
y4 = y(4);
F(1) = y2;
F(2) = Peh*(y2 + b*Da*y3*exp(-1/y1) - U*(yw-y1));
F(3) = y4;
F(4) = Pem*(y4 + Da*y3*exp(-1/y1));
F = F(:);
end
function f = mybc(ya,yb, Pem, Peh, yf)
% global Pem Peh yf
f(1) = ya(2)+Peh*(yf-ya(1));
f(2) = yb(2);
f(3) = ya(4) + Pem*(1-ya(3));
f(4) = yb(4);
f=f(:);
end
function g = guess(z) % initial guess for y and y'
g = [0.5
0.5
0.5
0.5];
end
Experiment to get different results.
.
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