Receiving Errors On Matrix Dimensions

2018 4 18
1 个回答
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更新时间：2018 4 24
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0 个投票

Hello, I am unsure if I am making a simple mistake but I am receiving errors for matrix size within my equation code. Here is the code:
for
Z = 0.1
W_n = 2.5;
B = sqrt(1 - Z^2);
Theta = atan(B/Z);
c(t) = 1 - (1/B) * exp(1) .^ -(Z * W_n * t) * sin(B * W_n * t + Theta);
end
I am receiving these error messages:
Error using * Inner matrix dimensions must agree.
Error in FeedbackControlSystem (line 65) c(t) = 1 - (1/B) * exp(1) .^ -(Z * W_n * t) * sin(B * W_n * t + Theta);
Error using ^ One argument must be a square matrix and the other must be a scalar. Use POWER (.^) for elementwise power.
Error in FeedbackControlSystem (line 65) c(t) = 1 - (1/B) * exp(1)^-(Z * W_n * t) * sin(B * W_n * t + Theta);
Any help would be greatly appreciated. Thank you!

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KSSV
KSSV 2018-4-18
What is t here?
Veera Kanmani
Veera Kanmani 2018-4-18
c(t) = 1 - (1/B) * exp(1) .^ -(Z * W_n * t) * sin(B * W_n * t + Theta);.. i think the problem occurs, can you specify code in detail manner and what is t value ?
Jacob Hammer
Jacob Hammer 2018-4-24

This is the updated code: (Also I apologize for the response time)

for

t = linspace(1,3600,360000)

c = zeros(1,360000);

Z = 0.1;

W_n = 2.5;

B = sqrt(1 - Z^2);

Theta = atan(B/Z);

 c(t) = 1 - ((1/B) * (exp(1) .^ -(Z * W_n .* t)) * (sin(B * W_n .* t + Theta)));

end

I am trying to simulate a feedback control system and c(t) was a given equation.

These are the variables:

B = Beta % Beta value will change with each section

% B = sqrt(1 - Z^2)

% Z = Zeta % Zeta value will change with each section

% W_n = natural frequency % Natural frequency will change with each % section

% Theta = theta % Theta in radians

% Theta = atan(B/Z)

% tan(Theta) = B/Z

Jacob Hammer
Jacob Hammer 2018-4-24
Updated Error Prompt:
>> FeedbackControlSystem Subscript indices must either be real positive integers or logicals.
Error in FeedbackControlSystem (line 67) c(t) = 1 - ((1/B) * (exp(1) .^ -(Z * W_n .* t)) * (sin(B * W_n .* t + Theta)));

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Ameer Hamza
Ameer Hamza 2018-4-24

1 个投票

From your code in the comment section, It can be seen that you are making a couple of mistakes.
  • t contain non-integers and thus can't be used to index c. In fact in this case you don't need to initialize c with zeros since it will not bring any speed up. Pre-allocation is only useful if your array size is changing in every loop iteration, here you can avoid that as given in below code snippet.
  • Not taking care of matrix dimension when multiplying. In MATLAB * is for matrix multiplication and .* is for element-wise multiplication. (exp(1) .^ -(Z * W_n .* t)) is 1*360000 and (sin(B * W_n .* t + Theta))) is also 1*360000. Therefore you need .* operation between them.
t = linspace(1,3600,360000);
Z = 0.1;
W_n = 2.5;
B = sqrt(1 - Z^2);
Theta = atan(B/Z);
c = 1 - ((1/B) * (exp(1) .^ -(Z * W_n .* t)) .* (sin(B * W_n .* t + Theta)));

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Jacob Hammer
Jacob Hammer 2018-4-24
When using this specific code, c yields 1. Shouldn't c yield a matrix of the same dimensions as t?
Jacob Hammer
Jacob Hammer 2018-4-24
Correction: When eliminating the for loop, c yields a matrix of the same dimensions as t, but consists of only 1's
Jacob Hammer
Jacob Hammer 2018-4-24
Pardon the second correction but I just realized my time vector is much too large to see the actual fluctuations within the plot. Thank you for your help.
Ameer Hamza
Ameer Hamza 2018-4-24

Yes, t and c have same dimensions. But the range of t is rather too large to see anything useful in plot. You might want to reduce the range of t.

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