pdf {DISTRIB}

Probability density function (pdf) and probability mass function (pmf)

Description

This function compute the value of Probability Density/Mass Function (pdf/pmf) for any univariate distribution at point t, i.e. f(t) for continues random variable T, or P(T = t) for discrete random variable. Unlike the common pdf's/pmf's of other distributions (such as dnorm, dpois and etc.) the name of the introduced pdf function is fix for any distribution and the name of distribution is considered as an argument of this function. So the pdf function is applicable for any kind of distribution with an unique form but by considering the name of T distribution (and its parameters) as two arguments of pdf function.

Usage

pdf(T.dist, T.dist.par, t)

Arguments

T.dist

The distribution name of the random variable is determined by characteristic element T.dist. The names of distributions is similar to stats package.

T.dist.par

A vector of distribution parameters with considered ordering in stats package.

t

A real number or a vector of real numbers. pdf compute pdf/pmf of a distribution in point t.

Value

This function gives the value of probability density function (pdf) at point t for continues random variable, or gives the value of probability mass function (pmf) at point t for discrete random variable.

Examples

pdf(T.dist="norm", T.dist.par=c(0,1), t=0) # Is equal to  dnorm(0)
pdf(T.dist="t", T.dist.par=c(7), -2) # Is equal to  dt(-2,7)
pdf(T.dist="pois", T.dist.par=5, 5) # Is equal to  dpois(5,5)


## The function is currently defined as
function (T.dist, T.dist.par, t) 
{
    dDis = paste("d", T.dist, sep = "", collapse = "")
    if (length(T.dist.par) == 1) {
        pdf.t = do.call(dDis, list(t, T.dist.par[1]))
    }
    else {
        if (length(T.dist.par) == 2) {
            pdf.t = do.call(dDis, list(t, T.dist.par[1], T.dist.par[2]))
        }
        else {
            pdf.t = do.call(dDis, list(t, T.dist.par[1], T.dist.par[2], 
                T.dist.par[3]))
        }
    }
    return(pdf.t)
  }