我想使用 R 和 lpSolve 解决一个优化问题,类似于 Excel 中的求解器插件。下面是一个简单的案例,其中我想要最大化 npv 值,具体地使用 lpSolve。
df <- structure(list(id = c(1, 2, 3, 4, 5, 6, 7, 8), Revenue = c(109, 111, 122, 139, 156, 140, 137, 167)), row.names = c(NA, 8L), class = "data.frame")
dcf <- function(x, r, t0=FALSE){
# calculates discounted cash flows (DCF) given cash flow and discount rate
#
# x - cash flows vector
# r - vector or discount rates, in decimals. Single values will be recycled
# t0 - cash flow starts in year 0, default is FALSE, i.e. discount rate in first period is zero.
if(length(r)==1){
r <- rep(r, length(x))
if(t0==TRUE){r[1]<-0}
}
x/cumprod(1+r)
}
npv <- function(x, r, t0=FALSE){
# calculates net present value (NPV) given cash flow and discount rate
#
# x - cash flows vector
# r - discount rate, in decimals
# t0 - cash flow starts in year 0, default is FALSE
sum(dcf(x, r, t0))
}
npv(df$Revenue,.2)
#Non optimized npv yields a value of 492.
#How can i use lpSolve to optimize my table? Said another way how can I rearrange the table to maximize npv using lpSolve?
更复杂的问题涉及到一列惩罚,其规则如下: Id 表示项目。
#Randomize order to give base npv. Now i need to optimize the order to find max value
df<- df%>%mutate(random_sort= sample(nrow(df)))
x=function(i){
df_fcn<- i
df_fcn<- df_fcn%>%mutate(Penalty= if_else(abs(random_sort-lag(random_sort))>2,1,.8))%>%mutate(Penalty=ifelse(is.na(Penalty),1,Penalty))
df_fcn<- df_fcn%>%mutate(Revenue_Penalized= Revenue*Penalty)
npv(df_fcn$Revenue_Penalized,.2)
}