每月按揭付款和摊销表计算

Question

我找到了一个示例代码，但我不明白星星里面的部分是什么。

我需要复制以下链接，并创建一个反映现金流量信息的现金流量表：

http://www.wolframalpha.com/input/?i=mortgage

我的主要问题是了解星星内的代码区域。

代码的具体部分如下，我理解计算，而不是正在进行的代码。

    # Calculate Amortization for each Month
if(amort==T) {
    Pt <- P # current principal or amount of the loan
    currP <- NULL
    while(Pt>=0) {
        H <- Pt * J # this is the current monthly interest
        C <- M - H # this is your monthly payment minus your monthly interest, so it is the amount of principal you pay for that month
        Q <- Pt - C # this is the new balance of your principal of your loan
        Pt <- Q # sets P equal to Q and goes back to step 1. The loop continues until the value Q (and hence P) goes to zero
        currP <- c(currP, Pt)
    }
    monthP <- c(P, currP[1:(length(currP)-1)])-currP
    aDFmonth <<- data.frame(
                      Amortization=c(P, currP[1:(length(currP)-1)]), 
                      Monthly_Payment=monthP+c((monthPay-monthP)[1:(length(monthP)-1)],0),
                      Monthly_Principal=monthP, 
                      Monthly_Interest=c((monthPay-monthP)[1:(length(monthP)-1)],0), 
                      Year=sort(rep(1:ceiling(N/12), 12))[1:length(monthP)]
            )
    ****aDFyear <- data.frame(
                     Amortization=tapply(aDFmonth$Amortization, aDFmonth$Year, max), 
                     Annual_Payment=tapply(aDFmonth$Monthly_Payment, aDFmonth$Year, sum), 
                     Annual_Principal=tapply(aDFmonth$Monthly_Principal, aDFmonth$Year, sum), 
                     Annual_Interest=tapply(aDFmonth$Monthly_Interest, aDFmonth$Year, sum), 
                     Year=as.vector(na.omit(unique(aDFmonth$Year)))
                     )
    aDFyear <<- aDFyear
    cat("The amortization data for each of the", N, "months are stored in \"aDFmonth\".\n\n")
    cat("The amortization data for each of the", L, "years are stored in \"aDFyear\".\n\n")******