I can't figure out why n=length(sigma) has gone wrong

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Samuel Walker
Samuel Walker 2021-3-8
评论： Walter Roberson 2021-3-9
function [V1,V2]=q3_test1(K,CD0,S,sigma,W,T0)
n = length(sigma);
V1=zeros(1,n);
V2=zeros(1,n);
for i = 1:n
T = T0*sigma(i);
rho = 1.225*sigma(i);
if T^2 < 4*K*CD0*W^2
V1 = -1;
V2 = -1;
else
X1 = (T-sqrt(T^2-4*K*CD0*W^2))/2*CD0;
V1 = sqrt(X1/(0.5*rho*S));
X2 = (T+sqrt(T^2-4*K*CD0*W^2))/2*CD0;
V2 = sqrt(X2/(0.5*rho*S));
end
end
end

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回答（1 个）

David Jacob
David Jacob 2021-3-8
What is the error message? What is the value for n?
  3 个评论
显示 1更早的评论
David Jacob
David Jacob 2021-3-8
Have you run the function properly by defining sigma first and then calling the function with sigma as an input?
Walter Roberson
Walter Roberson 2021-3-9
You cannot just run the code by pressing the green Run button.
Well, you can do that, but the result is the error message you see,
When you run a function, MATLAB will never look in the calling environment to see if a variable has been defined with the same name as a parameter that has not been passed in. So when you run the code by pressing the green Run button, MATLAB will not check the base workspace (or any other workspace) to see if it can find values for K, CD0, S, sigma, W, or T0 to use in the function.
There are some circumstances under which other variables might be looked for in the calling environment, but never for variables named in the list on the function statement.

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