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Granular matter describes large collections of small grains, under conditions in which the Brownian motion of the grains is negligible (sizes d>1 micrometer). The grains can exhibit solidlike behavior and fluidlike behavior, but the description of these states is still controversial. The present discussion is restricted to static problems, for which the main approach is to describe properly the initial state of each volume element, when it was deposited from a fluid flow.
P. G. de Gennes (Mon,) studied this question.