#' Updates one step of the Omega vector. Omega is  diagonal elements of the a variance covariance matrix.
#' usses the rTrunkInvGamma for sampling of the diagonal elements of Omega matrix
#' @param omega = omega's are positive elements arranged in decreasing order.
#' @param A= Beta rate parameters for the omega components. vector of length u. 
#' @param alpha= shape parameter for all the omega components.shape here is a scaler quantity.
#' @export
UpdateOmega<-function(omega,A,alpha,Max_rejection=100){
  #make sure that the omega components are in gereasing order.
  u=length(omega)
  omega_tmp=c(Inf,omega,0)
  for( i in 2:  (u+1)  ){
    #print(paste("OMEGA=",omega_tmp))
    omega_tmp[i]=rTrunkInvGamma(alpha=alpha,beta=A[i-1],l=omega_tmp[i+1],u=omega_tmp[i-1],Max_rejection=Max_rejection)
  }
  #print(omega_tmp)
  return(omega_tmp[2:(u+1)])
  
}