

Hello Charlie,
Thanks for your valuable help. You are right. So I changed tau_i=c(100,200,300,400) to tau_i=c(0,100,200,300) because "400" can be defined by another term. 
I appreciate for your time and knowledge.
Best,
JinNational Renewable Energy Lab.Golden CO, 80401(303) 275-4642jinsuk.lee@nrel.gov
Date: Thu, 25 Mar 2010 07:48:40 -0800
From: ml-node+1690861-886360020-66190@n4.nabble.com
To: realstone@hotmail.com
Subject: Re: how to deal with vector[0]?




Jin wrote:
Hi,


I have  a vector with 4 elements, e.g., tau_i=c(100,200,300,400), but potentially tau_i[0]=0. In a "for" loop,


tau_i=c(100,200,300,400)

m=4

tau_i[0]=0  # <------- ?

P_i=1

        for(i in 2:m)

        {

                P_i = P_i*(tau_i[i-1]-tau_i[i-2])

        }



Error in P_i = P_i * (tau_i[k - 1] - tau_i[k - 2]): 

  replacement has length zero



Unfortunately, I can add this potential element into "tau_i" because it has been defined initially and used mainly throughout all procedures.


When I calculate 

> k=2

> tau_i[k-1]-tau_i[k-2]

umeric(0)


But, it should be "100". Is there anyone can help me solve this problem?



Best,


Jin

NREL, Golden CO

(303) 275-4642


I'm a little confused on exactly what you're trying to achieve here-- vector indexes in R start at 1, not 0, and so trying to assign any value to tau_i[ 0 ] is meaningless.


Using tau_i[ 0 ] in a calculation is equivalent to using numeric( 0 ) -- i.e. a numeric vector of *length* zero, which contains no values at all.


Does this help?


-CçCharlie Sharpsteen

Undergraduate-- Environmental Resources Engineering

Humboldt State University





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