How can I solve the error "unable to convert to matrix form because the system does not seem to be linear"

I have 19 equations and 19 variables. I am trying to use equations to matrix to solve it, yet I get the error:

Error using mupadengine/feval_internal

Unable to convert to matrix form because the system does not seem to be linear.

Error in sym/equationsToMatrix (line 61)

T = eng.feval_internal('symobj::equationsToMatrix',eqns,vars);

Some of the variables in my equations are squared, for example:

eqn15=(ayAB)+((0.275.*sind(th)).*((OAP).^2))-((0.15.*cosd(th2)).*(al_AB))-((0.15.*sind(th2)).*((AB).^2))==0;

Are those squares the mistake? How could I solve a system of non-linear equations if necessary?

[KSSV]

Show us the whole code...so that we can check.

Answer 1

[I CHUN LIN]

You can not use matrix if the system is non-linear, maybe try fsolve or vpasolve.

The two-variables system example:

fun = @root2d;
x0 = [0,0];
x = fsolve(fun,x0)

function F = root2d(x)

F(1) = exp(-exp(-(x(1)+x(2)))) - x(2)*(1+x(1)^2);
F(2) = x(1)*cos(x(2)) + x(2)*sin(x(1)) - 0.5;
end

[Sebastián]

Thank you! I was able to get a solution using solve.