point characteristic function

point characteristic function

[′pȯint ‚kar·ik·tə′ris·tik ‚fəŋk·shən]
(optics)
The integral between two points of n ds along some path, where ds is the arc length of an infinitesimal piece of the path and n is the refractive index; according to Fermat's principle, it is a maximum or minimum with respect to nearby paths for the actual path of a light ray.
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