R/myncurve.R

In matthewCmatt/MATH4753CARROLL: Matt's Example Package

#' Graphs and calculates the lower tail probability of a in a normal distribution.
#'
#' @param a The number for which the probability of the lower tail will be found
#' @param mu The mean of the normal distribution
#' @param sigma The standard deviation of the normal distribution
#'
#' @return Lower tail probability of a. Prints graph visualizing the lower tail.
#' @export
#'
#' @examples
#' myncurve(0) -> 0.5

myncurve = function(a, mu=0, sigma=1){
  ## This is a code snippet taken from my Lab 6 Task 2 implementation and altered.

  #Define constants
  lowlim = mu-3*sigma
  upplim = mu+3*sigma

  #Plot base curve
  curve(dnorm(x, mean=mu,sd=sigma),xlim=c(lowlim, upplim))

  #Add polygon section of area.
  xcurve=seq(lowlim,a,length=1000)
  ycurve=dnorm(xcurve,mean=mu,sd=sigma)

  polygon(c(lowlim,xcurve,a),c(0,ycurve,0),col="Red")

  #Return accurate calculation of probability
  pnorm(a,mu,sigma)
}