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I learned yesterday that the inverse of square roots is used to calculate the vectors of surface normals in 3d graphics. It seems like such a mind-bogglingly simple idea, and it leads me to wonder if it hasn't found use elsewhere. Is there anywhere in physics where one might need to calculate the reciprocal of a number's square root?

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closed as not constructive by Qmechanic Feb 15 '13 at 15:57

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Multiplying by the reciprocal of the squareroot of the length squared, is a common method of normalizing vectors (in the L2 norm). Of course dividing by the square root is algebraically equivalent, but on a computer eliminates a rounding operation. Vectors that are normalized, are (somewhat) easier to work with.

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