solve non linear equation

I wrote a function to find value of x (with 3 unknown) by solving 3 equations described in F

a= [5 8 4 4];
b= [4 15 3 3];
c= [12 12 2 2];
x0=[0 0 0];

function F = myfun2(x)
F =  [sqrt((a(1)-x(1))^2+(a(2)-x(2))^2+(a(3)-x(3))^2)-(a(4)+4);
      sqrt((b(1)-x(1))^2+(b(2)-x(2))^2+(b(3)-x(3))^2)-(b(4)+4);
      sqrt((c(1)-x(1))^2+(c(2)-x(2))^2+(c(3)-x(3))^2)-(c(4)+4)];

Then I got the error after running this command

x=fsolve(@myfun2,x0)

??? Undefined function or method 'a' for input arguments of type 'double'.

Error in ==> myfun2 at 2
F =  [sqrt((a(1)-x(1))^2+(a(2)-x(2))^2+(a(3)-x(3))^2)-(a(4)+4);

Error in ==> fsolve at 254
            fuser = feval(funfcn{3},x,varargin{:});

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

anyone have any idea that what problem I have? And how to solve it?

Thanks a lot!!!

[Walter Roberson]

Please reformat your question.

Answer 1

[Walter Roberson]

The workspace of your function myfun2() does not have access to whichever workspace you defined "a" in.

Consider passing "a" and "b" in to the function myfun2(). Also consider defining myfun2() as a nested function with access to "a" and "b" as shared variables.

[The Anh]

Thank you so much for your fast answer, highly appreciate :)

Answer 2

[The Anh]

In case I work with a loop and a, b and c are variables and their values change in every loop. How can function "myfun2" have access to those variables?

How can I define mufun2() as a nested function with access to "a", "b" and "c" as share variables?