....1.1
Quantities such as and are often called process variables.
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... space''.2.1
The term is probably due to Paul Ehrenfest who in his classical book on Statistical Mechanics refers to -space, or molecular'' space as opposed to , or gas'' space (see Chapter 3 below).
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In an MD simulation not only the total energy but also the total momentum is conserved; this should be kept in mind when comparing simulation results to theoretical statements. Actually, the four conditions and , would define a -dimensional spherical shell in velocity space. However, for sufficiently numerous particles () this detail may be neglected, and we can base the argumentation just on the condition (with a -dimensional shell).
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... size3.2
A particularly powerful formulation of classical mechanics, known as Hamilton's formalism, makes use of the variables (position and momentum) in place of (position and velocity.) In this notation the phase space cells have the size .
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