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  2. Angstrom - Wikipedia

    en.wikipedia.org/wiki/Angstrom

    It was only in 1960, when the metre was redefined in the same way, that the angstrom became again equal to 10 −10 metre. Yet the angstrom was never part of the SI system of units, [ 13 ] [ 14 ] and has been increasingly replaced by the nanometre ( 10 −9 m) or picometre ( 10 −12 m).

  3. Symmetric mean absolute percentage error - Wikipedia

    en.wikipedia.org/wiki/Symmetric_mean_absolute...

    The earliest reference to a similar formula appears to be Armstrong (1985, p. 348), where it is called "adjusted MAPE" and is defined without the absolute values in the denominator. It was later discussed, modified, and re-proposed by Flores (1986). Armstrong's original definition is as follows:

  4. List of mathematical constants - Wikipedia

    en.wikipedia.org/wiki/List_of_mathematical_constants

    Foias constant is the unique real number such that if x 1 = ... 8, 1, 1, 10, 1, 1, 12 ... for rational x greater than or equal to one. before 1996 Metallic mean ...

  5. Percentage - Wikipedia

    en.wikipedia.org/wiki/Percentage

    In general, if an increase of x percent is followed by a decrease of x percent, and the initial amount was p, the final amount is p (1 + 0.01 x)(1 − 0.01 x) = p (1 − (0.01 x) 2); hence the net change is an overall decrease by x percent of x percent (the square of the original percent change when expressed as a decimal number).

  6. Mean squared error - Wikipedia

    en.wikipedia.org/wiki/Mean_squared_error

    The denominator is the sample size reduced by the number of model parameters estimated from the same data, (n−p) for p regressors or (n−p−1) if an intercept is used (see errors and residuals in statistics for more details). [7]

  7. Narcissistic number - Wikipedia

    en.wikipedia.org/wiki/Narcissistic_number

    In number theory, a narcissistic number [1] [2] (also known as a pluperfect digital invariant (PPDI), [3] an Armstrong number [4] (after Michael F. Armstrong) [5] or a plus perfect number) [6] in a given number base is a number that is the sum of its own digits each raised to the power of the number of digits.

  8. Probability amplitude - Wikipedia

    en.wikipedia.org/wiki/Probability_amplitude

    This leads to a constraint that α 2 + β 2 = 1; more generally the sum of the squared moduli of the probability amplitudes of all the possible states is equal to one. If to understand "all the possible states" as an orthonormal basis, that makes sense in the discrete case, then this condition is the same as the norm-1 condition explained above.

  9. Galileo's paradox - Wikipedia

    en.wikipedia.org/wiki/Galileo's_paradox

    Not only so, but the proportionate number of squares diminishes as we pass to larger numbers, Thus up to 100 we have 10 squares, that is, the squares constitute 1/10 part of all the numbers; up to 10000, we find only 1/100 part to be squares; and up to a million only 1/1000 part; on the other hand in an infinite number, if one could conceive of ...