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  2. Population density - Wikipedia

    en.wikipedia.org/wiki/Population_density

    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 ...

  3. Mulliken population analysis - Wikipedia

    en.wikipedia.org/wiki/Mulliken_population_analysis

    The sum of the gross orbital products is N - the total number of electrons. The Mulliken population assigns an electronic charge to a given atom A, known as the gross atom population: as the sum of over all orbitals belonging to atom A. The charge, , is then defined as the difference between the number of electrons on the isolated free atom ...

  4. Triangular distribution - Wikipedia

    en.wikipedia.org/wiki/Triangular_distribution

    Triangular. In probability theory and statistics, the triangular distribution is a continuous probability distribution with lower limit a, upper limit b, and mode c, where a < b and a ≤ c ≤ b .

  5. Multivariate normal distribution - Wikipedia

    en.wikipedia.org/wiki/Multivariate_normal...

    The multivariate normal distribution is said to be "non-degenerate" when the symmetric covariance matrix is positive definite. In this case the distribution has density [5] where is a real k -dimensional column vector and is the determinant of , also known as the generalized variance.

  6. Density matrix - Wikipedia

    en.wikipedia.org/wiki/Density_matrix

    v. t. e. 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 ...

  7. Median - Wikipedia

    en.wikipedia.org/wiki/Median

    The median of a finite list of numbers is the "middle" number, when those numbers are listed in order from smallest to greatest. If the data set has an odd number of observations, the middle one is selected. For example, the following list of seven numbers, has the median of 6, which is the fourth value.

  8. Probability density function - Wikipedia

    en.wikipedia.org/wiki/Probability_density_function

    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 ...

  9. Friedmann equations - Wikipedia

    en.wikipedia.org/wiki/Friedmann_equations

    The density parameter Ω is defined as the ratio of the actual (or observed) density ρ to the critical density ρ c of the Friedmann universe. The relation between the actual density and the critical density determines the overall geometry of the universe; when they are equal, the geometry of the universe is flat (Euclidean).