Why does my function keep returning zero?

Question

Prithvi Shams 2019-10-3

0
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https://ww2.mathworks.cn/matlabcentral/answers/483368-why-does-my-function-keep-returning-zero

评论： Rik 2019-10-3

In the following code, my objective is to plug different values of T and alpha into the functon and calculate y for two situations: when alpha < = 0.3 and when alpha > 0.3.

However, when I call the function in the command window, I keep getting y = 0. In fact, for whatever value of T and alpha I choose (in the context of the problem I'm trying to solve, T = 350 and alpha = 0.3), I get y = 0. If I remove y from the code and try to calculate just K1, K2, K3 by plugging different values of T into the function, I still get 0. What is wrong with the code?

function [y] = cure(T, alpha)
A1 = 2.101*10^8;
A2 = -2.014*10^9;
A3 = 1.96*10^5;
E1 = 8.07*10^4;
E2 = 7.78*10^4;
E3 = 5.66*10^4;
B = 0.47;
R = 8.31; %Universal gas constant
K1 = A1*exp(-(E1/R*T));
K2 = A2*exp(-(E2/R*T));
K3 = A3*exp(-(E3/R*T));
if alpha <= 0.3
    y = (K1 + K2*alpha)*(1 - alpha)*(B - alpha);
    
elseif alpha < 0.3
    
    y = K3(1 - alpha);
    
end
end

Here is how I tried to execute the function in the Command window,

[y] = cure(350, 0.3)

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Prithvi Shams 2019-10-3

Silly mistake on my part! Thanks a lot, solved the problem.

Rik 2019-10-3

Your conditionals almost overlap entirely.

In general it is a good idea to have an else statement with an error if you don't expect the else to ever be triggered. (same goes for switch and otherwise)

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