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  2. Estimation of covariance matrices - Wikipedia

    en.wikipedia.org/wiki/Estimation_of_covariance...

    The sample covariance matrix (SCM) is an unbiased and efficient estimator of the covariance matrix if the space of covariance matrices is viewed as an extrinsic convex cone in R p×p; however, measured using the intrinsic geometry of positive-definite matrices, the SCM is a biased and inefficient estimator. [1]

  3. Kendall rank correlation coefficient - Wikipedia

    en.wikipedia.org/wiki/Kendall_rank_correlation...

    The denominator is the total number of pair combinations, so the coefficient must be in the range −1 ≤ τ ≤ 1.. If the agreement between the two rankings is perfect (i.e., the two rankings are the same) the coefficient has value 1.

  4. Cochran's theorem - Wikipedia

    en.wikipedia.org/wiki/Cochran's_theorem

    The following version is often seen when considering linear regression. [4] Suppose that (,) is a standard multivariate normal random vector (here denotes the n-by-n identity matrix), and if , …, are all n-by-n symmetric matrices with = =.

  5. Backtracking line search - Wikipedia

    en.wikipedia.org/wiki/Backtracking_line_search

    The method involves starting with a relatively large estimate of the step size for movement along the line search direction, and iteratively shrinking the step size (i.e., "backtracking") until a decrease of the objective function is observed that adequately corresponds to the amount of decrease that is expected, based on the step size and the ...

  6. Bitcoin - Wikipedia

    en.wikipedia.org/wiki/Bitcoin

    The limited block size and frequency can lead to delayed processing of transactions, increased fees and a bitcoin scalability problem. [99] The Lightning Network , second-layer routing network, is a potential scaling solution.

  7. Internal rate of return - Wikipedia

    en.wikipedia.org/wiki/Internal_rate_of_return

    Internal rate of return (IRR) is a method of calculating an investment's rate of return.The term internal refers to the fact that the calculation excludes external factors, such as the risk-free rate, inflation, the cost of capital, or financial risk.

  8. Cargo - Wikipedia

    en.wikipedia.org/wiki/Cargo

    Air freight shipments are very similar to LTL shipments in terms of size and packaging requirements. However, air freight or air cargo shipments typically need to move at much faster speeds than 800 km or 497 mi per hour.

  9. University of Arizona - Wikipedia

    en.wikipedia.org/wiki/University_of_Arizona

    The University of Arizona (Arizona, U of A, UArizona, or UA) is a public land-grant research university in Tucson, Arizona, United States.Founded in 1885 by the 13th Arizona Territorial Legislature, it was the first university established in the Arizona Territory.