fsolve yields initial guess as solution to non-linear equation
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I am currently trying to solve a non-linear equation using the following program:
clc; format long g;
a=0.5; Eta0=100; t12=1e6; q=2e-7; R=0.001;
A=pi*(R^4)/(8*Eta0); B=4/(3+a); C=0.5*R/t12;
But no matter what value of initial guess I choose, the program always gives THAT value as the root of this equation. Here the soultion would be x=1e6, but the program yields any value that I enter as x0, which in this case is 8e5.
I have tested the routine with solutions that are smaller numbers (order of magnitude of (1-10), but when the solutions becomes a relatively large number this problem occurs.
Davide Masiello on 13 Feb 2022
Try with this syntax
clc, format long g
a = 0.5;
Eta0 = 100;
t12 = 1e6;
q = 2e-7;
R = 0.001;
x0 = 14e5;
Px = fzero(@(x)F1(x,q,Eta0,a,t12,R),x0);
Now the value found is always the same regardless of x0, provided that x0 is not too far from the root.