Fsolve giving incorrect answers
Show older comments
Hello
I'm trying to solve this system:
x = a + e(c - e*x/((x^2+y^2)^(3/2))), y = b + c(d - e*y/((x^2+y^2)^(3/2)))
I'm using Fsolve, but not matter what i put in as the startpoints for the iteration i get the answer as the startpoints.
close all, clear all, clc
a = 1;
b = 2;
c = 3;
d = 4;
e = 5;
fsolve(@u1FsolveFUNC,[1,2])
Function:
function outvar = u1FsolveFUNC(invar)
global a b c d e
outvar = [-invar(1) + a + e*(c - e*(invar(1) / ((invar(1)^2 + invar(2)^2)^(3/2)))) ; -invar(2) + b + e*(d - e*(invar(2) / ((invar(1)^2 + invar(2)^2)^(3/2))))]
end
I could try with [1,2] as invariables, and it will say that that is a root to the equation, alltough the correct answer for [1,2] is [12.76,15.52]
Ideas?
2 Comments
SdiM
on 10 Jun 2013
Roger Stafford
on 11 Jun 2013
I would like to point out that if the equations you have shown being entered into 'fsolve' are what you intended, then 'fsolve' is not actually needed. Those equations can be solved using 'roots'.
If r is any positive real root of
r^6-((a+e*c)^2+(b+e*d)^2)*r^4+2*e^2*r^3+e^4 = 0
then
x = (a+e*c)/(1+e^2/r^3)
y = (b+e*d)/(1+e^2/r^3)
are solutions and r = sqrt(x^2+y^2). For the values of a,b,c,d,e you have given, there are two solutions:
(15.98007976343752,21.97260967472658)
and
(0.57425274904229,0.78959752993316)
However there is a disparity between these equations and those you originally stated. The two respective sets are:
x = a+e*(c-e*x/(x^2+y^2)^(3/2)), y = b+c*(d-e*y/(x^2+y^2)^(3/2))
x = a+e*(c-e*x/(x^2+y^2)^(3/2)), y = b+e*(d-e*y/(x^2+y^2)^(3/2))
differing by one parameter: c versus e. It isn't clear which one you intended to use and which was a typographical error.
Answers (0)
Categories
Find more on Matrix Decomposition in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!