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Density ( volumetric mass density or specific mass) is a substance's mass per unit of volume. The symbol most often used for density is ρ (the lower case Greek letter rho ), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume: [1] where ρ is the density, m is the mass, and V is the volume ...
In probability theory, a probability density function (PDF), density function, or density of an absolutely continuous random variable, is a function whose value at any given sample (or point) in the sample space (the set of possible values taken by the random variable) can be interpreted as providing a relative likelihood that the value of the random variable would be equal to that sample.
Relative density ( ) or specific gravity ( ) is a dimensionless quantity, as it is the ratio of either densities or weights. where is relative density, is the density of the substance being measured, and is the density of the reference. (By convention , the Greek letter rho, denotes density.) The reference material can be indicated using ...
Population density is the number of people per unit of area, usually transcribed as "per square kilometer" or square mile, and which may include or exclude, for example, areas of water or glaciers. Commonly this is calculated for a county, city, country, another territory or the entire world . The world's population is around 8,000,000,000 [3 ...
Natural density. In number theory, natural density, also referred to as asymptotic density or arithmetic density, is one method to measure how "large" a subset of the set of natural numbers is. It relies chiefly on the probability of encountering members of the desired subset when combing through the interval [1, n] as n grows large.
In quantum mechanics, a density matrix (or density operator) is a matrix that describes the quantum state of a physical system. It allows for the calculation of the probabilities of the outcomes of any measurement performed upon this system, using the Born rule. It is a generalization of the more usual state vectors or wavefunctions: while ...
v. t. e. Given two random variables that are defined on the same probability space, [1] the joint probability distribution is the corresponding probability distribution on all possible pairs of outputs. The joint distribution can just as well be considered for any given number of random variables. The joint distribution encodes the marginal ...
The following are examples, using two common distribution functions, of how applying a distribution function to the density of states can give rise to physical properties. Figure 4: The Fermi-Dirac probability distribution, density of states, and their product for a semiconductor.