diffQuot <- function(x,y)
{
  stopifnot(length(x)==length(y))
  
  l <- length(x)
  
  dq <- numeric(l)
  
  dq[1] <- (y[2] - y[1])/(x[2] - x[1])
  dq[2:(l-1)] <- (y[3:l] - y[1:(l-2)])/(x[3:l] - x[1:(l-2)])
  dq[l] <- (y[l] - y[l-1]) / (x[l] - x[l-1])
  
  return(dq)
}