In mathematical terms, as in common parlance, a signal is something that conveys information. Jordan Ellenberg, a mathematician at the University of Wisconsin-Madison who first met Daubechies in 1998 when they were colleagues at Princeton, points out that signal processing “makes up a huge proportion of applied math now, since so much of applied math is about the geometry of information as opposed to the geometry of motion and force” — that is, it’s more about the warp and weft of information than physical problems in, say, fluid dynamics or celestial mechanics.
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