how to get rid of imaginary numbers, after a root.

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oskar
oskar 2013-10-25
评论： Kumaresh Kumaresh 2022-6-14
hi, i´m a beginner in matlab and i have been making a tracejtory with a basketball. my problem now is with the time.
This is a part of my script. My speed and angle are two vectors, because of the vectors sometimes the roots will be an imaginary number and (at=atand....) will get error. How do I do if i only want real numbers to go into at=atand....
time = roots([-g./2, v0y, y0-H]);
time = max(time);
at=atand((h0*cos(V))/((h0*sin(V))-(g*tid)));
thanks for your time=)

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采纳的回答

Muruganandham Subramanian
time = roots([-g./2, v0y, y0-H]);
time = max(time);
time=real(time);
at=atand((h0*cos(V))/((h0*sin(V))-(g*tid)))

更多回答（2 个）

Simon
Simon 2013-10-25
Hi!
What do you expect, physically? Your trajectory is a parabola with negative prefactor in front of t^2. So, the apex is the highest point of your curve. If it is negative you won't find real roots of the polynom. Pyhsically this means you throw your ball from below the earth's surface and it is falling downwards ... ;-)
oskar
oskar 2013-10-25
I know, thats why i have two vectors wich will eventually get it into the baskethoop, but when the all the numbers "time" is going into the at=atand... i don't want the imaginary numbers to go into at=atand...
  1 个评论
Simon
Simon 2013-10-25
If you just want to skip the atand command for imaginary time you may surround it with
if isreal(time)
atand ...
end

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