How can i polt the negative values in my code?

Hello im strugling to find a way to plot my code here

clc
clear

%Motor Parameters
V1 = 469.5;
nph = 3;
poles = 4;
fe = 60;

R1 = 0.9174;
X1 = 0.005473*2*pi*fe;

Xm = 0.1854*2*pi*fe;

X2 = 0.005473*2*pi*fe;
R2 = 0.6258;

%Calculating syncronus speed

omegas = 4*pi*fe/poles;
ns = 120*fe/poles;

%Stator thenvenin equivelent

Z1eq = 1i*Xm*(R1 + 1i*X1)/(R1 + 1i* (X1+Xm));
R1eq = real(Z1eq);
X1eq = imag(Z1eq);

V1eq = abs(V1*1i*Xm/(R1 +1i*(X1 + Xm)));

%Slip loop

for x = 1:200

      s(x) = x/50;
      rpm(x) = ns*(1-s(x));
      I2 = abs(V1eq/(Z1eq + 1i*X2 + R2/(s(x))));
      Tmech(x) = nph*(I2^2)*R2/(s(x)*omegas);
  end

plot(Tmech,rpm)

xlabel('Tmech')
ylabel('rpm')

it is a torque-speed graph for a motor. i con not figure our how i can get negative values of x and always giving me Array indices must be positive integers or logical values.

Error in Speed_torqe_graphing (line 37) s(x) = x/50;

any help is really appreciated.

Answer 1

[Adam Danz]

Instead of using x to represent the values you'd like to test, use x as the index values of a vector 'q' that contains the values you'd like to test.

Replace your for-loop with this to test values -200 to 200

%Slip loop
q = -200:1:200; 
for x = 1:length(q)
      s(x) = q(x)/50;
      rpm(x) = ns*(1-s(x));
      I2 = abs(V1eq/(Z1eq + 1i*X2 + R2/(s(x))));
      Tmech(x) = nph*(I2^2)*R2/(s(x)*omegas);
  end

[ update] You don't need the for-loop, by the way. All of the code above can rewritten as:

q = -200:1:200;
s = q/50; 
rmp = ns * (1-s); 
I2 = abs(V1eq./(Z1eq + 1i*X2 + R2./s));
Tmech = nph*(I2.^2)*R2./(s.*omegas);

[Omar Elcircevi]

You sir are a big life saver, thank you!