Undefined function or variable 'x'.

similar to the question am also having the same doubt

function F = myfun(x)
x=[x(0),x(1),x(2),x(3),x(4),x(5)];
F = [2*x(1) - x(2) - exp(-x(1));
-x(1) + 2*x(2) - exp(-x(2))];
h=str2func( ['@myfun' F] );
fsolve(h,x1);

this is an example problem from matlab.am just trying to solve this.but am getting error as i mentioned in question!!!!!

how can eliminate this error

my equation is consists of 5 variable and lengthy equation for example my first equation is * *

((((-x(1)*x(2)*x(4)) + (x(1)*x(3)*x(5))*0.15335) + (0.0680154*(-x(1)*x(2)*x(4)) + (x(3)*x(1)*x(5))) + (x(1) (x(1)*x(2)) + (x(2)*x(3)))*(-0.15335))*(1 + (x(1)+(x(1)*x(2)) + (x(2)*x(3)))*0.15335) - ((0.1067*(x(1)*x(2)*x(4)) + (x(1)*x(3)*x(5))) + (x(1) + (x(1)*x(2)) + (x(2)*x(3))*0.0340077)))]

so i need to solve my equations

help to solve the problem

Answer 1

[Steven Lord]

Do NOT try to call FSOLVE with a function handle to myfun from within myfun itself. Doing so is likely to lead to a recursion error. Either create two separate function files, one named myfun.m that evaluate the system of equations for which you want to find a solution and another that contains your FSOLVE call. The solveit.m file should contain only:

 function y = solveit(x0)
 % Contains the FSOLVE call ONLY
 y = fsolve(@myfun,x0);

and the myfun.m file should contain only:

 function F = myfun(x)
 % Contains the system to be solved
 F = [2*x(1) - x(2) - exp(-x(1));
      -x(1) + 2*x(2) - exp(-x(2))];

Alternately, if the only place you use myfun is in this solveit call, you could create it as a subfunction in solveit.m to avoid creating two separate files. In this scenario, solveit.m contains:

 function y = solveit(x0)
 y = fsolve(@myfun,x0);

 function F = myfun(x)
 F = [2*x(1) - x(2) - exp(-x(1));
      -x(1) + 2*x(2) - exp(-x(2))];

In either of these cases, you'd call solveit with your initial guess at a solution vector as the only input.

[Yahia Mounir]

Thanks Steven for your explanation can you have a look for attached file and equation and try fix the m.file I will be grateful for your help

Answer 2

[Julia]

Is it "Undefined function or variable 'x'" or "Undefined function or variable 'x1'"?

fsolve(h, x1);

I cannot find x1 in your code.

[sabarish]

i need to solve the another set of equation like i mentioned above passage

its showing error

could u please hep to rectify

its showing error like this

tail11 at 2
F=[((x(1)*(-x(2)*x(4))+(x(3)*x(5))*0.15335)+(x(1)*(1+x(2)+x(3))))/((1+(x(1)*(1+x(2)+x(3))*0.1535)^2));

Error in ==> fsolve at 248
            fuser = feval(funfcn{3},x,varargin{:});

Caused by:
    Failure in initial user-supplied objective function evaluation. FSOLVE cannot     continue.

Answer 3

[Image Analyst]

You did not define x1. Also you can't start with and index of zero like you did. To crop/extract only the first 6 elements of x, you'd do this

x = x(1:6);

[sabarish]

its showing again error like this

Input argument "x" is undefined.

Error in ==> tail11 at 2 x = x(1:6);

[Image Analyst]

Attach your m-file so we can fix it.

Answer 4

[Yahia Mounir]

Hello I am trying to run the following file however it give me error undefined variable X, I attached the my file can you help with that ,

Please note if i call the function at command window with the following steps @myfun t x0=[0 0] x=(@myfun,xo) it is working and giving me the answer i need only to use the mfile to get the answer

[Walter Roberson]

The file did not get attached.