MATLAB: How to Nonlinear equations?(two variables)

circuitnonlinear

f(1) = x(1)*(14+r1)-10*x(2)-4*x(3)-100;
f(2) = x(1)*-10+x(2)(18+r2)+x(3)*-8+80;
f(3) = x(1)*-4+x(2)*-8+x(3)*12-50;
how can I solve these nonlinear equations. There are rheostatic values so there is a second variable t. Should I write a function?eq

Best Answer

Although R1 and R2 are nonlinear finctions of t, your equations are linear in x. So you write the equations on the form
A(t)*x = b and solve by x = A\b for every t of interest.
I suggest you define R1(t) and R2(t) as anonymous functions. Here is a template:
R1 = @(t) 5*t^2+10;
R2 = @(t) 2*exp(t)+5;
t = linspace(0,5);
b = [100;-80+8;50];
X= zeros(3,length(t));
for i = 1:length(t)
  A = [3 by 3 matrix containing R1(t(i)) and R2(t(i))];
  X(:,i) = A\b;
end
plot(t,X')
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