solve constraint optimization problem

I want to solve constraint optimization problem :

min||M||^2 , where the norm is the frobinus norm and M is 2×2 matrix =[1 x;x 1+2x]

i wrote like that but i got error

x = optimvar('x');
prob = optimproblem;
M=[1 x;x 1+2*x]
prob.Objective = norm(M,'fro')^2;
prob.Constraints.cons1 = x^2-2*x <=1
prob.Constraints.cons2 = x >=- 1/2;

sol = solve(prob,x)

Answer 1

[Torsten]

x = optimvar('x');
prob = optimproblem;
M=[1 x;x 1+2*x];
prob.Objective = norm(M,'fro')^2;
prob.Constraints.cons1 = x^2-2*x <=1;
prob.Constraints.cons2 = x >=- 1/2;
x0.x = 1;

sol = solve(prob,x0)

Solving problem using fmincon.

Local minimum found that satisfies the constraints.

Optimization completed because the objective function is non-decreasing in 
feasible directions, to within the value of the optimality tolerance,
and constraints are satisfied to within the value of the constraint tolerance.

sol = struct with fields:
    x: -0.3333

[Hajar Alshaikh]

I copied your code and got this message :

Unable to perform assignment because dot indexing is not supported for variables of this type.

[Torsten]

Then you use an older MATLAB version.

Take a look at your older documentation on how to supply initial values for the solution variables.