MATLAB: Hi I am trying to solve a system of equations using fsolve or something similar with 4 variables. Please help

44 variablesfsolvemyfunnon-linear equationsnonlinear

Equations are

r(1)= sqrt((x-15600)^2+(y-7540)^2+(z-20140)^2)-(300000(0.07074-d))
r(2)=sqrt((x-18760)^2+(y-2750)^2+(z-18610)^2)-(300000(0.07220-d))
r(3)=sqrt((x-17610)^2+(y-14630)^2+(z-13480)^2)-(300000(0.07690-d))
r(4)=sqrt((x-19170)^2+(y-610)^2+(z-18340)^2)-(300000(0.07242-d))

I am trying to use fsolve

F=nle(x) ; I am actually substitution x,y,z,d as x(1)….x(4)

Then writing the equation for F and then i do x0= a range which i dont understand at all what to pick.

And then fsolve(@nle,x0)

I am getting a lot of errors and nowhere near to my answer.

Best Answer

Rishav, try

 function r = test(r0)
 % options  = optimoptions('fsolve','Display','iter');  % new as of R2013a
 % options  = optimset('Display','iter','TolFun',1e-8); % before R2013a
 % [r,fval] = fsolve(@myfun,r0,options)                
 [r,fval] = fsolve(@myfun,r0)
 end
 function F = myfun(r)
 x = r(1);
 y = r(2);
 z = r(3);
 d = r(4);
 F = [sqrt((x-15600)^2+(y-7540)^2 +(z-20140)^2)-(300000*(0.07074-d));... 
      sqrt((x-18760)^2+(y-2750)^2 +(z-18610)^2)-(300000*(0.07220-d));...
      sqrt((x-17610)^2+(y-14630)^2+(z-13480)^2)-(300000*(0.07690-d));...
      sqrt((x-19170)^2+(y-610)^2  +(z-18340)^2)-(300000*(0.07242-d))];
 end

and use in the MATLAB command window

 r0 = [15000 10000 20000 0];
 r  = test(r0)

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MATLAB: I continue to receive an error message when I try to use fsolve. Can anyone tell me what I’m doing wrong? (I’m using MATLAB R2012a)

You made some coding errors. Note that x1 is not the same as x(1). Also, if you look closely at the documentation for fsolve, all your unknown variables have to be members of the same vector. I reformatted your code:

x(1) = 15600; y(1) = 7540; z(1) = 20140;
x(2) = 18760; y(2) = 2750; z(2) = 18610;
x(3) = 17610; y(3) = 14630; z(3) = 13480;
x(4) = 19170; y(4) = 610; z(4) = 18390;
t(1) = 0.07074; t(2) = 0.07220; t(3) = 0.07690; t(4) = 0.07242;
c = 299792458;
x0 = [1 1 1 1];
% myfun325_1 = @(x,y,z,d)  [sqrt(((x - x(1)).^2) + ((y - y(1)).^2) + ((z - z(1)).^2)) - c*(t(1) - d); sqrt(((x - x(2)).^2) + ((y - y(2)).^2) + ((z - z(2)).^2)) - c*(t(2) - d); sqrt(((x - x(3)).^2) + ((y - y(3)).^2) + ((z - z(3)).^2)) - c*(t(3) - d); sqrt(((x - x(4)).^2) + ((y - y(4)).^2) + ((z - z(4)).^2)) - c*(t(4) - d);];
% Redefine x, y, z, d as p(1) ... p(4)
myfun325_1 = @(p)  [sqrt(((p(1) - x(1)).^2) + ((p(2) - y(1)).^2) + ((p(3) - z(1)).^2)) - c*(t(1) - p(4)); sqrt(((p(1) - x(2)).^2) + ((p(2) - y(2)).^2) + ((p(3) - z(2)).^2)) - c*(t(2) - p(4)); sqrt(((p(1) - x(3)).^2) + ((p(2) - y(3)).^2) + ((p(3) - z(3)).^2)) - c*(t(3) - p(4)); sqrt(((p(1) - x(4)).^2) + ((p(2) - y(4)).^2) + ((p(3) - z(4)).^2)) - c*(t(4) - p(4));];
estp = fsolve(myfun325_1, x0);
x = estp(1)
y = estp(2)
z = estp(3)
d = estp(4)

It ran without problems. (I did not change anything else in myfun325_1.)

MATLAB: I am getting a straight line while running the following code. What is going wrong?

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y=exp(-x.^2/2)./sqrt(x);
plot(x,y)

It's ./ instead of /

Best Answer

Related Solutions

MATLAB: I continue to receive an error message when I try to use fsolve. Can anyone tell me what I’m doing wrong? (I’m using MATLAB R2012a)

MATLAB: I am getting a straight line while running the following code. What is going wrong?

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