MATLAB Answers

0

Plotting the solution of multi-variable non-linear equations (solved using fsolve).

Asked by Yavar Hayat on 9 Apr 2019
Latest activity Commented on by Yavar Hayat on 10 Apr 2019
These are the equations:
function [fval]= ptfunc(X)
Tcell=X(1);
Pcell=X(2);
Qh=X(3);
Pteg=X(4);
alpha = 0.95;
A = (0.04)^2;
epsilon = 0.88;
sigma = 5.69*10^(-8);
Ta = 298.15;
u=(0.003+1/5)^-(1);
ns = 0.10;
theta = 0.0011;
An=6.4*10^-7;
Hn=0.01;%:0.01:0.06;
N=62;
S=185*10^-6;
rho=10^-5;
den=2*rho;
k=1.5;
Z=(S^2)/(rho.*k);
Tc=298;
r=0.2;
n=0.0001;
hc=0.00009;
num2=2*r*hc;
G=500;
fval(1,1)= -Qh+ alpha*G*A-u*A*(Tcell-Ta)-epsilon*sigma*A*((Tcell.^4)-(Ta^4))-Pcell;
fval(2,1)= -Pcell+ alpha*G*A*ns.*(1-theta.*(Tcell - 298));
fval(3,1)= -Qh + (k*An*N/Hn)*(1-Z*(3*Tcell+Tc)/8)*(Tcell-Tc);
fval(4,1)= -Pteg+(S^2)*An*N*((Tcell-Tc)^2)./(den.*(n+Hn).*(1+num2./Hn).^2);
I need to plot the varaibles with respect to G. How do I do that?

  2 Comments

G is a scalar - its value is 500 - so you would plot 4 single points - one for each result from fsolve. Is this what you want to do?
No. I want to the values of G so as to plot the four variables accordglingly.

Sign in to comment.

Tags

Products


Release

R2017b

1 Answer

Answer by Torsten
on 9 Apr 2019
 Accepted Answer

function main
G = linspace(250,750).';
X0 = [1,1,1,1];
for i=1:numel(G)
sol = fsolve(@(X)ptfunc(X,G(i)),X0);
x(i,:) = sol;
X0 = sol;
end
plot(G,x(:,1))
end
function fval = ptfunc(X,G)
Tcell=X(1);
Pcell=X(2);
Qh=X(3);
Pteg=X(4);
alpha = 0.95;
A = (0.04)^2;
epsilon = 0.88;
sigma = 5.69*10^(-8);
Ta = 298.15;
u=(0.003+1/5)^-(1);
ns = 0.10;
theta = 0.0011;
An=6.4*10^-7;
Hn=0.01;%:0.01:0.06;
N=62;
S=185*10^-6;
rho=10^-5;
den=2*rho;
k=1.5;
Z=(S^2)/(rho.*k);
Tc=298;
r=0.2;
n=0.0001;
hc=0.00009;
num2=2*r*hc;
%G=500;
fval(1,1)= -Qh+ alpha*G*A-u*A*(Tcell-Ta)-epsilon*sigma*A*((Tcell.^4)-(Ta^4))-Pcell;
fval(2,1)= -Pcell+ alpha*G*A*ns.*(1-theta.*(Tcell - 298));
fval(3,1)= -Qh + (k*An*N/Hn)*(1-Z*(3*Tcell+Tc)/8)*(Tcell-Tc);
fval(4,1)= -Pteg+(S^2)*An*N*((Tcell-Tc)^2)./(den.*(n+Hn).*(1+num2./Hn).^2);
end

  4 Comments

Show 1 older comment
However, it is working. The reason it does not look like it is working is that one of the results is on the order of 300, and two of them are on the order of 0.1, and the last of them is on the order of 0.01 . You simply cannot see anything in 3 of the 4 lines because they are insignificant on the scale of the first plot.
You could use subplot() to break the values out.
If you have a new enough MATLAB you could use stackedplot()
I got it by using
plot(G,x(:,1))
plot(G,x(:,2))
etc.
Thank you.

Sign in to comment.