curretal88explc <- function(xx)
{
  ##########################################################################
  #
  # CURRIN ET AL. (1988) EXPONENTIAL FUNCTION, LOWER FIDELITY CODE
  # Calls: curretal88exp.r
  # This function, from Xiong et al. (2013), is used as the "low-accuracy
  # code" version of the function curretal88exp.r.
  #
  # Authors: Sonja Surjanovic, Simon Fraser University
  #          Derek Bingham, Simon Fraser University
  # Questions/Comments: Please email Derek Bingham at dbingham@stat.sfu.ca.
  #
  # Copyright 2013. Derek Bingham, Simon Fraser University.
  #
  # THERE IS NO WARRANTY, EXPRESS OR IMPLIED. WE DO NOT ASSUME ANY LIABILITY
  # FOR THE USE OF THIS SOFTWARE.  If software is modified to produce
  # derivative works, such modified software should be clearly marked.
  # Additionally, this program is free software; you can redistribute it 
  # and/or modify it under the terms of the GNU General Public License as 
  # published by the Free Software Foundation; version 2.0 of the License. 
  # Accordingly, this program is distributed in the hope that it will be 
  # useful, but WITHOUT ANY WARRANTY; without even the implied warranty 
  # of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
  # General Public License for more details.
  #
  # For function details and reference information, see:
  # http://www.sfu.ca/~ssurjano/
  #
  ##########################################################################
  #
  # INPUT:
  # xx = c(x1, x2)
  #
  #########################################################################
  
  source('curretal88exp.r')

  x1 <- xx[1]
  x2 <- xx[2]
  
  maxarg <- max(c(0, x2-1/20))
  
  yh1 <- curretal88exp(c(x1+1/20, x2+1/20))
  yh2 <- curretal88exp(c(x1+1/20, maxarg))
  yh3 <- curretal88exp(c(x1-1/20, x2+1/20))
  yh4 <- curretal88exp(c(x1-1/20, maxarg))
  
  y <- (yh1 + yh2 + yh3 + yh4) / 4
  return(y)
}