R/GB2.R

In gamlss.dist: Distributions for Generalized Additive Models for Location Scale and Shape

# amended 1/12/2007
GB2 <- function (mu.link="log", sigma.link="log", nu.link ="log", tau.link="log")
{
    mstats <- checklink(   "mu.link", "Generalized beta 2 (i.e. of the second kind)", substitute(mu.link), 
                           c("1/mu^2", "log", "identity"))
    dstats <- checklink("sigma.link", "Generalized beta 2 (i.e. of the second kind)", substitute(sigma.link), 
                           c("inverse", "log", "identity"))
    vstats <- checklink(   "nu.link", "Generalized beta 2 (i.e. of the second kind)", substitute(nu.link),    
                           c("1/nu^2", "log", "identity"))
    tstats <- checklink(  "tau.link", "Generalized beta 2 (i.e. of the second kind)", substitute(tau.link),   
                           c("1/tau^2", "log", "identity")) 
    structure(
          list(family = c("GB2", "Generalized beta 2 (i.e. of the second kind)"),
           parameters = list(mu=TRUE, sigma=TRUE, nu=TRUE, tau=TRUE), 
                nopar = 4, 
                 type = "Continuous",
              mu.link = as.character(substitute(mu.link)),  
           sigma.link = as.character(substitute(sigma.link)), 
              nu.link = as.character(substitute(nu.link)), 
             tau.link = as.character(substitute(tau.link)), 
           mu.linkfun = mstats$linkfun, 
        sigma.linkfun = dstats$linkfun, 
           nu.linkfun = vstats$linkfun,
           tau.linkfun = tstats$linkfun,  
           mu.linkinv = mstats$linkinv, 
        sigma.linkinv = dstats$linkinv,
           nu.linkinv = vstats$linkinv,
           tau.linkinv = tstats$linkinv, 
                mu.dr = mstats$mu.eta, 
             sigma.dr = dstats$mu.eta, 
                nu.dr = vstats$mu.eta,
               tau.dr = tstats$mu.eta, 
    dldm = function(y,mu,sigma,nu,tau) 
                      { 
             z <- (y/mu)^sigma
          dldm <- -(sigma*nu)/mu + (sigma/mu)*(nu+tau)*z/(1+z)
          dldm
                      },
   d2ldm2 = function(y,mu,sigma,nu,tau)
                      {
        d2ldm2 <- -((sigma^2)*nu*tau)/((nu+tau+1)*mu^2)
        d2ldm2
                      },     
   dldd = function(y,mu,sigma,nu,tau)  
                      {  
             z <- (y/mu)^sigma
          dldd <- (1/(sigma)) + (nu/sigma)*log(z) - (nu+tau)*z*log(z)/(sigma*(1+z))
          dldd                     
                      },
   d2ldd2 = function(y,mu,sigma,nu,tau)
                      {
           d2a <- nu*(digamma(nu+1)-digamma(nu))
           d2b <- ((nu*tau)/(nu+tau+1))*(trigamma(nu+1)+trigamma(tau+1)+(digamma(nu)-
                    digamma(tau))^2)
        d2ldd2 <- -(d2a+d2b)/(sigma^2)
        d2ldd2
                      },   
     dldv = function(y,mu,sigma,nu,tau) 
                      { 
             z <- (y/mu)^sigma
          dldv <- log(z)-log(1+z)-digamma(nu)+digamma(nu+tau)
          dldv
                      },
    d2ldv2 = function(nu,tau) 
                      { 
         d2ldv2 <- trigamma(nu+tau) - trigamma(nu)
         d2ldv2
                      },
      dldt = function(y,mu,sigma,nu,tau) 
                      {
              z <- (y/mu)^sigma
           dldt <- -log(1+z)-digamma(tau)+digamma(nu+tau)
           dldt
                      },
      d2ldt2 = function(y,mu,sigma,nu,tau) 
                      { 
         d2ldt2 <- trigamma(nu+tau) - trigamma(tau)
         d2ldt2
                      },
  d2ldmdd = function(mu,nu,tau) 
                      {
        d2ldmdd <- ((nu*tau)/((nu+tau+1)*mu))*(digamma(nu+1)-digamma(tau+1))
        d2ldmdd 
                      },
  d2ldmdv = function(mu,sigma,nu,tau) 
                      {
       d2ldmdv <- -(sigma*tau)/(mu*(nu+tau))
       d2ldmdv
                      },
  d2ldmdt = function(mu,sigma,nu,tau) 
                      {
       d2ldmdt <- (sigma*nu)/(mu*(nu+tau))
       d2ldmdt
                      },
  d2ldddv = function(y,mu,sigma,nu,tau) 
                      {
      d2ldddv <- -(nu/(sigma*(nu+tau)))*(digamma(nu+1)-digamma(tau))+
                   (1/sigma)*(digamma(nu)-digamma(tau))
      d2ldddv
                      },
  d2ldddt = function(y,mu,sigma,nu,tau) 
                      {
      d2ldddt <- -(nu/(sigma*(nu+tau)))*(digamma(nu+1)-digamma(tau))
      d2ldddt
                      },
  d2ldvdt = function(nu,tau) 
                      {
     d2ldvdt <- trigamma(nu+tau)
     d2ldvdt
                      },
 G.dev.incr  = function(y,mu,sigma,nu,tau,...) 
                      { 
             -2*dGB2(y,mu,sigma,nu,tau,log=TRUE)
                      } ,                     
         rqres = expression(   
               rqres(pfun="pGB2", type="Continuous", y=y, mu=mu, sigma=sigma, nu=nu, tau=tau)) ,
    mu.initial = expression(mu <- (y+mean(y))/2),    
 sigma.initial = expression(sigma<- rep(0.1, length(y))),  
    nu.initial = expression(nu <- rep(1, length(y))), #0.03
   tau.initial = expression(tau <-rep(1, length(y))), #0.02
      mu.valid = function(mu) all(mu > 0), 
   sigma.valid = function(sigma)  TRUE,
      nu.valid = function(nu) all(nu > 0), 
     tau.valid = function(tau) all(tau > 0), 
       y.valid = function(y)  TRUE,
          mean = function(mu, sigma, nu, tau) ifelse(tau > 1/sigma, mu * beta(nu + 1/sigma, tau - 1/sigma) / beta(nu,tau), Inf),
      variance = function(mu, sigma, nu, tau) ifelse(tau > 2/sigma, mu^2 * (beta(nu + 2/sigma,tau - 2/sigma) * beta(nu,tau) - (beta(nu + 1/sigma, tau - 1/sigma))^2) / (beta(nu, tau))^2, Inf)
          ),
            class = c("gamlss.family","family"))
}
#-----------------------------------------------------------------
dGB2 <- function(x, mu = 1, sigma = 1, nu = 1, tau = .5, log = FALSE)
 {
          if (any(mu < 0))  stop(paste("mu must be positive", "\n", "")) 
          if (any(nu < 0))  stop(paste("nu must be positive", "\n", ""))  
          if (any(tau < 0))  stop(paste("tau must be positive", "\n", ""))  
       z <- (x/mu)^sigma
       loglik <- nu*log(z)+log(abs(sigma))-log(x)-lgamma(nu)-lgamma(tau)+
       lgamma(nu+tau)-(nu+tau)*log(1+z)
       if(log==FALSE) ft  <- exp(loglik) else ft <- loglik 
       ft <- ifelse(x <= 0, 0, ft)
       ft
  }    
#-----------------------------------------------------------------  
pGB2 <- function(q, mu = 1, sigma = 1, nu = 1, tau = .5, lower.tail = TRUE, log.p = FALSE)
 {  
      if (any(mu < 0))  stop(paste("mu must be positive", "\n", "")) 
      if (any(nu < 0))  stop(paste("nu must be positive", "\n", ""))  
      if (any(tau < 0))  stop(paste("tau must be positive", "\n", ""))           
      z <- (q/mu)^sigma
      w <- (tau/nu)*z 
      p <- pf(w,2*nu,2*tau)
    if (length(sigma)>1)  p <- ifelse(sigma<0,1-p,p)
    else p <- if (sigma<0) 1-p else p
      if(lower.tail==TRUE) p  <- p else  p <- 1-p 
      if(log.p==FALSE) p  <- p else  p <- log(p) 
      p
 }
#-----------------------------------------------------------------  

qGB2 <-  function(p, mu=1, sigma=1, nu=1, tau=.5, lower.tail = TRUE, log.p = FALSE)
 {   
    if (any(mu < 0))  stop(paste("mu must be positive", "\n", "")) 
    if (any(nu < 0))  stop(paste("nu must be positive", "\n", ""))  
    if (any(tau < 0))  stop(paste("tau must be positive", "\n", ""))  
    if (log.p==TRUE) p <- exp(p) else p <- p
    if (any(p <= 0)|any(p >= 1))  stop(paste("p must be between 0 and 1", "\n", ""))       
    if (lower.tail==TRUE) p <- p else p <- 1-p
    if (length(sigma)>1)  p <- ifelse(sigma<0,1-p,p)
    else p <- if (sigma<0) 1-p else p
    w <- qf(p,2*nu,2*tau)   
    q <- mu*(((nu/tau)*w)^(1/sigma))
    q
 }
#-----------------------------------------------------------------  
rGB2 <- function(n, mu=1, sigma=1, nu=1, tau=.5)
  {
    if (any(mu < 0))  stop(paste("mu must be positive", "\n", "")) 
    if (any(nu < 0))  stop(paste("nu must be positive", "\n", ""))  
    if (any(tau < 0))  stop(paste("tau must be positive", "\n", ""))  
    n <- ceiling(n)
    p <- runif(n)
    r <- qGB2(p,mu=mu,sigma=sigma,nu=nu,tau=tau)
    r
  }
#-----------------------------------------------------------------