discrete
This entry aims at highlighting the fact that all uses of the word discrete in mathematics are directly related to the core concept of discrete space:
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A discrete set is a set that, endowed with the topology
implied by the context, is a \\PMlinkescaptetextdiscrete space. For instance for a subset of and without information suggesting otherwise, the topology on the set would be assumed the usual topology induced by norms on .
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A random variable is discrete if and only if its image space is a discrete set (which by what’s just been said means that the image is a discrete topological space for some topology specified by the context). The most common example by far is a random variable taking its values in a enumerated set (e.g. the values of a die, or a set of possible answers to a question in a survey).
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Discretization of ODEs and PDEs is the process of converting equations on functions on open sets of (with boundary conditions
) into equations on functions on discrete subsets of .