## Special Functions of Mathematics

## Usage

    beta(a, b)
    lbeta(a, b)
    gamma(x)
    lgamma(x)
    digamma(x)
    trigamma(x)
    tetragamma(x)
    pentagamma(x)
    choose(n,k)
    lchoose(n,k)

## Description

The functions `beta` and `lbeta` return the beta function and the natural logarithm of the beta function,

B(a,b) = (Gamma(a)Gamma(b))/(Gamma(a+b)).

The functions `gamma` and `lgamma` return the gamma function &Gamma(x) and the natural logarithm of the absolute value of the gamma function.

The functions `digamma`, `trigamma`, `tetragamma` and `pentagamma` return the first, second, third and fourth derivatives of the logarithm of the gamma function.

The functions `choose` and `lchoose` return binomial coefficients and their logarithms.

## See Also

`Arithmetic` for simple and `Math` for miscellaneous mathematical functions.

## Examples

    choose(5, 2)
    for (n in 0:10) print(choose(n, k = 0:n))

    curve(gamma(x),-3,4, n=1001, ylim=c(-10,100),
          col="red", lwd=2, main="gamma(x)")
    abline(h=0,v=0, lty=3, col="midnightblue")

    x <- seq(.1, 4, length = 201); dx <- diff(x)[1]
    par(mfrow = c(2, 3))
    for (ch in c("", "l","di","tri","tetra","penta")) {
      is.deriv <- nchar(ch) >= 2
      if (is.deriv) dy <- diff(y) / dx
      nm <- paste(ch, "gamma", sep = "")
      y <- get(nm)(x)
      plot(x, y, type = "l", main = nm, col = "red")
      abline(h = 0, col = "lightgray")
      if (is.deriv) lines(x[-1], dy, col = "blue", lty = 2)
    }
    par(mfrow = c(2, 2))

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