** Generate sphere. **

** [X,Y,Z] = SPHERE(N) generates three (n+1)-by-(n+1) **

** matrices so that SURF (X,Y,Z) produces a unit sphere. **

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** [X,Y,Z] = SPHERE uses N = 20. **

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** SPHERE(N) and just SPHERE graph the sphere as a SURFACE **

** and do not return anything. **

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** See also CYLINDER . **

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