How to solve for each value a SOLVE equation

Qout is a line matrix [1*cont] and I want to obtain a solution for x for each Qout and to store that information in some new matrix. How can I do this? Thank you very much!

x = []; 
for i=1:1:cont
  eqn = @(x)  Qout(i) == Ks*(d^2 * (2*x - sin(2*x)) / 8)*((d * (1 - sin(2*x) / 2*x) / 4)^(2/3))*sqrt(s) ;
  solve(eqn,x)
  x1(i)=x
end

when I run the code above I get a error message:

 Error using solve>getEqns (line 414)
    The input contains an empty equation or variable.
 Error in solve (line 225)
    [eqns,vars,options] = getEqns(varargin{:});
 Error in Ficha3_1 (line 112)
    solve(eqn,x)

Sorry if it's missing information but I'm quite noob at this.

Answer 1

[Star Strider]

I would not use the Symbolic Math Toolbox for this, and use the Optimization Toolbox fsolve function or the core MATLAB function fzero instead.

Try this:

x0 = 1;
x1 = nan(1,cont);
for i=1:1:cont
    eqn = @(x)  Qout(i) - ( Ks*(d^2 * (2*x - sin(2*x)) / 8)*((d * (1 - sin(2*x) / 2*x) / 4)^(2/3))*sqrt(s) );
    x1(i) fsolve(eqn, x0);
end

Note — There are an infinity of solutions because ‘x’ is an argument to the sin() function. This example code will only find the solution closest to the initial estimate ‘x0’ in each iteration of the loop.

[Rebeca Marini]

Thank you so much! It worked perfectly!!

[Star Strider]

As always, my pleasure!