Figure does not display graph

Hello,

I am trying plot a graph of power out over power in (efficiency) for a motor, and I am sure that my equations are correct however, the resulting figure is empty. I tried to bug fix and got rid of the semi-colon after the line of code and found that the was only getting a single value for the variable (0.2423, which sounds about right), I don't understand how MATLAB has computed this value as P_out and P_in are both functions of the torque, and hence the resulting must also be a function of the torque. I am certain that my equations for power out and power in are correct, I think that there is an issue when matlab divides a quadratic function by a linear function. Below is my code:

v = 24; %voltage = 24 V
r = 0.7; %resistance = 0.7 ohms
j = 7.95e-5; %inertia of the rotor = 7.95e-5 kgm^2
k = 0.059; %motor constant = 0.059 Vs/rad
b = 6.65e-5; %damping coefficient = Nms/rad
l = 9.8e-4; %inductance = 9.8e-4 H
i = 0.4494; %steady state current = 0.4494 A
w = 400; %steady state angular velocity = 400 rad/s
T_l = 0; %Torque applied to the motor = 0; 
time_period = 0.0014; %time period of the circuit = 0.0014 s

torque = 0:0.01:2.03;
torque_E = -5:0.1:5;
W = (v*k-torque*r)/(r*b+k^2); %angular velocity of the rotor as a function of the torque

I = (b/k)*W +torque/k; %current through motor as a function of the torque

P_out = torque.*W; %power output by the motor

P_in = v*I; %power into the motor

E = (P_out/P_in)

figure 
plot(torque, W, 'blue') %angular velocity plot against torque
ylim([0 400]);
x0 = interp1(W,torque,0); % stall torque for motor 1 (x-intercept of the torque axis) = 2.0229.

figure
plot(torque, I, 'red') %current plot against torque


figure 
plot(torque, P_out, 'magenta'); %power out plot against torque
ylim([0 250]);

figure
plot(torque, E, 'green'); %effecincy against torque

Answer 1

[KSSV]

Replace the lines:

plot(x,y,'red')

with

plot(x,y,'color','red')

Make these changes:

plot(torque, W,'color', 'blue') %angulaof r velocity plot against torque
ylim([0 400]);
x0 = interp1(W,torque,0); % stall torque for motor 1 (x-intercept of the torque axis) = 2.0229.
figure
plot(torque, I,'color', 'red') %current plot against torque
figure 
plot(torque, P_out, 'color','magenta'); %power out plot against torque
ylim([0 250]);
figure
plot(torque, E, 'color','green'); %effecincy against torque

Read about the documentation of plot.

[Tb]

That didn't change anything, the other 3 plots remain as visible whilst the efficiency plot remains invisible and only outputs a single value of 0.2423.

[KSSV]

You have to replace the line:

E = (P_out/P_in)

with

E = (P_out./P_in) 

You have to use element by element divison.

[Tb]

Ah yes, that sorts the issue out, I was aware of .* but wasn't aware of ./ thank you for the help.

[KSSV]

Thanks is accepting the answer .. :)