A~ha~!! Thank you, Prof. Peter Dalgaard, so much for your wonderful
lesson!!! Learning new things everyday from this R-help mailing list!
Chel Hee Lee
On 2/11/2015 10:37 AM, peter dalgaard wrote:
On 11 Feb 2015, at 17:11 , Chel Hee Lee <chl...@mail.usask.ca> wrote:
The functional form given in the post written by Ssuhanchen captures my eyes.
It is the cumulative distribution function of Poisson when the number of counts
is less than or equal to 2 with unknown parameter mu=x/2. Since it is a
nonlinear function, there may be multiple solutions but the solution should be
greater than 0 (if I am in the right track). I am assuming this functional
form is originated from the Poisson. Under this assumption, one solution is
found as below:
rt <- uniroot(function(x) ppois(2, lambda=x)-0.05, interval=c(0.5,1),
extendInt="yes")
Warning messages:
1: In ppois(2, lambda = x) : NaNs produced
2: In ppois(2, lambda = x) : NaNs produced
3: In ppois(2, lambda = x) : NaNs produced
ppois(2, lambda=rt$root)
[1] 0.0500001
rt$root
[1] 6.295791
Thus, the solution x would be rt$root*2 (Note that I did not try to find other
solutions). I hope this helps.
Given the Poisson connection, I would pretty strongly expect the solution to be
unique.
Notice also that your rt$root comes out as the upper end of the confidence
interval in
poisson.test(2, alt="l")
Exact Poisson test
data: 2 time base: 1
number of events = 2, time base = 1, p-value = 0.9197
alternative hypothesis: true event rate is less than 1
95 percent confidence interval:
0.000000 6.295794
sample estimates:
event rate
2
Chel Hee Lee
On 2/10/2015 2:29 AM, Rolf Turner wrote:
On 10/02/15 14:04, Ssuhanchen wrote:
Hi!
I want to use R to calculate the variable x which is in a complex equation
in below:
2
Σ[exp(-x/2)*(x^k)/(2^k*k!)]=0.05
k=0
how to solve this equation to get the exact x in R?
Is this homework? Sure looks like it. Talk to your prof. Or do a bit of work
on learning how to use R --- which is presumably the point of the exercise.
cheers,
Rolf Turner
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