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.*

source files: [cx]lsp.[ch]

SYNTAX

(.* <vector> <vector>)

DESCRIPTION

This operator returns the dot-product of the two <vector>s:

(.* (list x0 y0 z0) (list x1 y1 z1))

returns

x0 * x1   +   y0 * y1   +   z0 * z1

The dot-product of two unit vectors is a convenient way to compute the cosine of the angle between them. Taking the dotproduct of an arbitrary vector with a unit vector is a handy way of projecting it onto, for example, the coordinate axes. The SQRT of dotproduct of vector with itself gives you the length of the vector. The dotproduct of two nonnull vectors is zero iff the vectors are perpendicular, which makes dotproduct a handy test for perpendicularity. Since a plane can be regarded as defined by all vectors perpendicular to a given vector, this is also one way to approach the plane equation ...


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