where do those imaginary values come from?

Question

Evelyn 2014-3-18

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/122083-where-do-those-imaginary-values-come-from

回答： Image Analyst 2014-3-18

If I use this piece of code

b=24;                                                                      
k=2000*3600;                                                               
t=0:1:720;
Q_y = zeros(size(t));
for i = 1:length(t)
    if t(i) < 360-b/2
        Q_y(i) = (k/(360-b/2))*t(i);
    elseif t(i) >= 360-b/2 && t(i) < 360+b/2
        Q_y(i) = k;
    else
        Q_y(i) = (-k/(360-b/2))*t(i)+720*(k/(360-b/2));
    end
end

on itself everything is fine, but when I try to use it in a bigger piece of code Q_y suddenly gets imaginary values. Where do they come from and what can I do about them?