one-line

Factorial

  • the number of ways to order n unique items.

  • n! = (n)(n-1)...(1)

  • 0!=1, since there is only one way to order 0 items.

Multiply

  • rescale

  • multiplication

2x2 ^ x

  • step growth = next step, double the current

exe ^ x

  • natural growth = consider each part, grow little by little

Statistics

variance and standard deviation = dispersion

expected value = long-term average

covariance = two variables have same changes or not

Binomial / Bernoulli / Poisson

皆是Yes or No events

  • binomial = discrete occurrences among discrete trials. (擲骰子10次, n=10n = 10)

  • poisson = discrete occurrences among a continuous domain. (5年一次地震, nn \rightarrow \infty)

  • bernoulli = single Binomial event

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