TransfoParam_GR4J.R

TransfoParam_GR4J <- function(ParamIn,Direction){

  NParam <- 4;
  Bool <- is.matrix(ParamIn);
  if(Bool==FALSE){ ParamIn <- rbind(ParamIn); }
  if(ncol(ParamIn)!=NParam){ stop(paste("the GR4J model requires ",NParam," parameters \n",sep="")); return(NULL); }  

  if(Direction=="TR"){
    ParamOut     <-  ParamIn;
    ParamOut[,1] <- exp(ParamIn[,1]);                    ### GR4J X1 (production store capacity)    
    ParamOut[,2] <- sinh(ParamIn[,2]);                   ### GR4J X2 (groundwater exchange coefficient)      
    ParamOut[,3] <- exp(ParamIn[,3]);                    ### GR4J X3 (routing store capacity)       
    ParamOut[,4] <- 20+19.5*(ParamIn[,4]-9.99)/19.98;    ### GR4J X4 (unit hydrograph time constant)
  }	
  if(Direction=="RT"){
    ParamOut     <-  ParamIn;
    ParamOut[,1] <- log(ParamIn[,1]);                    ### GR4J X1 (production store capacity)    
    ParamOut[,2] <- asinh(ParamIn[,2]);                  ### GR4J X2 (groundwater exchange coefficient)      
    ParamOut[,3] <- log(ParamIn[,3]);                    ### GR4J X3 (routing store capacity)       
    ParamOut[,4] <- 9.99+19.98*(ParamIn[,4]-20)/19.5;    ### GR4J X4 (unit hydrograph time constant)
  }	

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

}