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November 19th, 2008, 05:28 PM  #1 
Newbie Joined: Nov 2008 Posts: 1 Thanks: 0  check if set of nonlinear equ. has only the trivial solution
Hi guys, When I solve equations 3,4,5,6 I'm getting small values for x(1),x(2),x(3),x(4). Using fsolve in matlab I tried different starting values x0, and solutions are in the order of 1e3 and depend on the starting value. How can I tell if the small values are approximating the trivial solution (because of limited accuracy during the calculation), or if there are several solutions close to the trivial solution? Since I know that there is only the trivial solution when using equation 1,2,3,4,5,6 I calculated x solving all equations and found x in the order of 1e9. In summary, I want to find out if there is only the trivial solution when solving equations 3,4,5,6. c2=0.27215029; c3=0.09718148; c5=2.62373636; c6=0.80306059; a1 = 0.2525 a2 = 0.0543 a3 = 0.0264 (1) c2*x(1)+c3*x(3)=0 (2) c2*x(2)+c3*x(4)=0 (3) c5*x(1)+c6*x(3)=0 (4) c5*x(2)+c6*x(4)=0 (5) a1*x(1)*x(2)+a2*x(3)*x(4)a3*(x(1)*x(4)+x(2)*x(3))=0 (6) a1*(x(2)^2x(1)^2)+a2*(x(4)^2x(3)^2)2*a3*(x(2)*x(4)x(1)*x(3))=0 Best Regards, Peter matlab code: x0 = [rand(1);rand(1);rand(1);rand(1)]; options=optimset('Display','iter','TolFun',1e20 ); % Option to display output [x,fval] = fsolve(@my_fun,x0,options); function F=my_fun(x) c2=0.27215029; c3=0.09718148; c5=2.62373636; c6=0.80306059; a1 = 0.2525 a2 = 0.0543 a3 = 0.0264 F=[ c2*x(1)+c3*x(3); c2*x(2)+c3*x(4); c5*x(1)+c6*x(3); c5*x(2)+c6*x(4); a1*x(1)*x(2)+a2*x(3)*x(4)a3*(x(1)*x(4)+x(2)*x(3)); a1*(x(2)^2x(1)^2)+a2*(x(4)^2x(3)^2)2*a3*(x(2)*x(4)x(1)*x(3))]; 

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check, equ, nonlinear, set, solution, trivial 
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