R/qgamma_mix.R

In matheuscastro43/finiteMix: Finite Mixture Models

qgamma_mix <- function(p, pi, alpha, beta, lower.tail = TRUE, log.p = FALSE){
  if(length(p) == 1){
    g <- length(pi)
    pi = pi/sum(pi)
    if(min(c(pi, alpha, beta)) > 0 && length(alpha) == g &&
       length(beta) == g){
      if(log.p){
        p = exp(p)
      }
      if(!lower.tail){
        p = 1 - p
      }
      if(p < 0 || p > 1){
        warning("The probability must be in (0, 1) interval.")
        return(NaN)
      }
      else{
        if(p == 0){return(0)}
        else{
          if(p == 1){return(Inf)}
          else{
            U = aux = 100
            h <- function(q){
              pgamma_mix(q, pi, alpha, beta) - p
              }
            while(aux >= 0.9*U){
              U = 2*U
              aux = uniroot(h, lower = 0, upper = U)$root
            }
            return(aux)
          }
        }
      }
    }else stop("The parametric space must be respected.")
    
  }else{
    j <- function(p){qgamma_mix(p, pi, alpha, beta, lower.tail, log.p)}
    return(sapply(p, j))
  }
}