#**************************************************************************************************
#' Function which transforms model parameters (from real to transformed parameters and vice versa).
#**************************************************************************************************
#' @title   Transformation of the parameters from the GR6J model
#' @author  Laurent Coron (December 2013)
#' @seealso \code{\link{TransfoParam}}, \code{\link{TransfoParam_GR4J}}, \code{\link{TransfoParam_GR5J}}, \code{\link{TransfoParam_CemaNeige}}
#' @example tests/example_TransfoParam_GR6J.R
#' @encoding UTF-8
#' @export
#_FunctionInputsOutputs____________________________________________________________________________
#' @param   ParamIn   [numeric] matrix of parameter sets (sets in line, parameter values in column)
#' @param   Direction [character] direction of the transformation: use "RT" for Real->Transformed and "TR" for Transformed->Real
#' @return  \emph{ParamOut} [numeric] matrix of parameter sets (sets in line, parameter values in column)
#**************************************************************************************************
TransfoParam_GR6J <- function(ParamIn,Direction){

  NParam <- 6;
  Bool <- is.matrix(ParamIn);
  if(Bool==FALSE){ ParamIn <- rbind(ParamIn); }
  if(ncol(ParamIn)!=NParam){ stop(paste("the GR6J model requires ",NParam," parameters \n",sep="")); return(NULL); }  

  if(Direction=="TR"){
    ParamOut     <-  ParamIn;
    ParamOut[,1] <- exp(1.5*ParamIn[,1]);                ### GR6J X1 (production store capacity)
    ParamOut[,2] <- sinh(ParamIn[,2]);                   ### GR6J X2 (groundwater exchange coefficient 1)
    ParamOut[,3] <- exp(ParamIn[,3]);                    ### GR6J X3 (routing store capacity)
    ParamOut[,4] <- 20+19.5*(ParamIn[,4]-9.99)/19.98;    ### GR6J X4 (unit hydrograph time constant)
    ### ParamOut[,5] <- sinh(Xtran[,5]);                   ### GR6J X5 (groundwater exchange coefficient 2)
    ParamOut[,5] <- ParamIn[,5]/5;                       ### GR6J X5 (groundwater exchange coefficient 2)
    ParamOut[,6] <- exp(ParamIn[,6]);                    ### GR6J X6 (coefficient for emptying exponential store)
  }	
  if(Direction=="RT"){
    ParamOut     <-  ParamIn;
    ParamOut[,1] <- log(ParamIn[,1]) / 1.5;              ### GR6J X1 (production store capacity)
    ParamOut[,2] <- asinh(ParamIn[,2]);                  ### GR6J X2 (groundwater exchange coefficient 1)
    ParamOut[,3] <- log(ParamIn[,3]);                    ### GR6J X3 (routing store capacity)
    ParamOut[,4] <- 9.99+19.98*(ParamIn[,4]-20)/19.5;    ### GR6J X4 (unit hydrograph time constant)
    ### ParamOut[,5] <- asinh(ParamIn[,5]);                  ### GR6J X5 (groundwater exchange coefficient 2)
    ParamOut[,5] <- ParamIn[,5]*5;                       ### GR6J X5 (groundwater exchange coefficient 2)
    ParamOut[,6] <- log(ParamIn[,6]);                    ### GR6J X6 (coefficient for emptying exponential store)
  }	

  if(Bool==FALSE){ ParamOut <- ParamOut[1,]; }
  return(ParamOut);

}