Unable to perform assignment because the left and right sides have a different number of elements.

I am trying to plot w, Pc, and F as functions of time following an iterative process but keep getting this error. How do I make them have the same number of elements?

clear all
close all
clc

hold on

for T = 1:1:101
  t = (T-1)/5;
    w(T) = 0.514 .* t; % Web Distance
    Ab(T) = (2 .* pi) .* (((144-(3 + w).^2)) + ((3 + w) .* 20) + ((144-(3 + w).^2))) % Burn Area       
    Pc(T) = (1088000 .* Ab ./ (400000000 .* pi)).^(1/0.7); % Chamber Pressure       
    rb(T) = 0.4 .* Pc.^0.3; % Burn Radius      
    F(T) = Pc .* pi .* 8000000; % Thrust Force
    if w > 9
        break
    else
        continue
    end
end

plot(w);
xlim([0 90])
ylim([0 10])

title('Web Distance vs. Time')
xlabel('Time (s)')
ylabel('Web Distance')

plot(Pc);
xlim([0 90])
ylim([0 5])

title('Chamber Pressure vs. Time')
xlabel('Time (s)')
ylabel('Chamber Pressure')

plot(F);
xlim([0 90])
ylim([0 10])

title('Thrust vs. Time')
xlabel('Time (s)')
ylabel('Thrust')

hold off

[DGM]

On the second pass, w is a vector. The RHS of that assignment is a vector. The LHS is a scalar. If you're trying to use a specific element of w (e.g. w(T-1)), you'll have to make that change.

[Student]

How would I make that change?

[DGM]

It's up to you to decide which elements you're trying to use. Decide which one you want and specify the appropriate index instead of the entire vector.

Answer 1

[Prateek Rai]

To my understanding, you want to plot w, Pc and F as functions of time follwing an interactive process.

You are getting an error because you are assigning array to a scalar quantity in line 8, line 9, line 10 and line 11 which causes error from 2nd iteration.

A possible workaround could be assigning the particular value of array (most proably the current value of array) to scalar quantity in above mentioned lines.

The code would look like:

clear all
close all
clc
hold on
for T = 1:1:101
  t = (T-1)/5;
    w(T) = 0.514 .* t % Web Distance
    Ab(T) = (2 .* pi) .* (((144-(3 + w(T)).^2)) + ((3 + w(T)) .* 20) + ((144-(3 + w(T)).^2))) % Burn Area       
    Pc(T) = (1088000 .* Ab(T) ./ (400000000 .* pi)).^(1/0.7); % Chamber Pressure       
    rb(T) = 0.4 .* Pc(T).^0.3; % Burn Radius      
    F(T) = Pc(T) .* pi .* 8000000; % Thrust Force
    if w > 9
        break
    else
        continue
    end
end
plot(w);
xlim([0 90])
ylim([0 10])
title('Web Distance vs. Time')
xlabel('Time (s)')
ylabel('Web Distance')
plot(Pc);
xlim([0 90])
ylim([0 5])
title('Chamber Pressure vs. Time')
xlabel('Time (s)')
ylabel('Chamber Pressure')
plot(F);
xlim([0 90])
ylim([0 10])
title('Thrust vs. Time')
xlabel('Time (s)')
ylabel('Thrust')
hold off