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

Question

Student 2022-2-22

0
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https://ww2.mathworks.cn/matlabcentral/answers/1655680-unable-to-perform-assignment-because-the-left-and-right-sides-have-a-different-number-of-elements

回答： Prateek Rai 2022-2-24

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

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Student 2022-2-22

How would I make that change?

DGM 2022-2-22

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.

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Answer 1

Prateek Rai 2022-2-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1655680-unable-to-perform-assignment-because-the-left-and-right-sides-have-a-different-number-of-elements#answer_903755

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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