在运行以下程序时，出现报错：Error in `[<-`(`*tmp*`, f, 1, value = 1 - quantile(y[20, ], 0.01)) :   subscript out of bounds。百思不得解，请各位指点一二，多谢！

P0 <- 15.51 ;mean.logret <- -0.000485681; sd.logret <- 0.053224794;  steps <- 20; paths <- 1000
set.seed(2000)
y<-matrix(NA,20,1000)
m=1
n=1
f=1
Var<-matrix(NA,20,1)
while(f<=30){
while(m<=20){
  while(n<=1000){
    P0=P0+P0*(mean.logret/20/20+0.011901426*rnorm(1,0,1)*0.223606798)
    y[m,n]<-P0
    n<-n+1}
  n=1
  m<-m+1}
Var[f,1]<- P0-quantile(y[20,],0.01)
m<-m+1
n=1
m=1
f<-f+1}