##ծȯ۸
bpd<-function(cf,par,y,n){
  t=1:n
  a=cf/(1+y)^t
  b=par/(1+y)^n
  p=sum(a,b)
}
##
byield<-function(n,cf,bp){
 accu=1e-5
 maxinter=200
 bot=0.00;top=1.00
 while(res>bp) {top=top*2}
 y=0.5*(top+bot)
for (i in 0:maxinter) {
  diff=res-bp
  if (abs(diff)<accu) {return(y)}
  if (diff>0.0) 
    bot=y
  else
    top=y
  y=0.5*(top+bot)
}
 {return(y)}
}

##par=100,cf=2.5,n=10,p=110,ծȯĵy