Help me about sphere ?

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Nguyen Trong Nhan
Nguyen Trong Nhan 2014-5-27
评论： Nguyen Trong Nhan 2014-5-27
I have this code to draw haft of sphere x^2 + y^2 + z^2 = 1, z>0. but it have error. help me to fix it. thanks very much.

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回答（1 个）

Mischa Kim
Mischa Kim 2014-5-27
编辑：Mischa Kim 2014-5-27
Nguyen, use instead
z = real(sqrt(1 - x.^2 - y.^2));
to retain the real part only.
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Mischa Kim
Mischa Kim 2014-5-27
编辑：Mischa Kim 2014-5-27
In a perfect world, yes. However, in numerical computations zero is not always (exactly) equal to zero. Check out this answer for reference. If you remove the semi-colon from
z = sqrt(1 - x.^2 - y.^2)
you'll notice that there are small non-zero imaginary parts.
Nguyen Trong Nhan
Nguyen Trong Nhan 2014-5-27
ah Mischa Kim, could you explain me when I need to use the eval and double funtions in matlab ?

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