问R中的差分方程

EN

 Ki <- function(a, t){ ## You need to actually define this properly
      return(1)
    }

    Ni <- function(a, t, PMF){
      if ((a %% 1 != 0)) stop("Only Takes Integer values of a")
      if ((t %% 1 != 0)) stop("Only Takes Integer values of t")

      if (a == 1){
        x = Ni(48, t-1, PMF)
        y = exp(-Ki(48,t-1))
        result = PMF * x * y
        return(result)
      }

      if (a > 1){
        x = Ni(a-1, t-1, PMF)
        y = exp(-Ki(a-1,t-1))
        result = x * y
        return(result)
      }
    }