# Fw: Re: Re: confidence interval/level

From: 朱学明 <557xiaozhu_at_nyahnyahspammersnyahnyah>
Date: Thu Sep 19 2013 - 12:10:46 MDT

Hi Dennis,
I am still confused on your example and do not know how to caculate spec@coher_probability exactly. Can you tell me what is the coh, why you set it as 0.5 in your example? Is it the confidence level(0.9, 0.95, 0.99) or spec@coher? What is the relationship between df and jave? Is df twice of jave?
Also, I found the formula
B=1-p**(1/(df/2-1)) (1)
from the reference, but your example is
p = 1.-(1.-coh)**(df/2.-1.) (2)

why are they different? Is the p in (2) same as p or B in (1) ? Which one is the spec@coher_probability from the function specxy_anal in NCL?

Thanks.

2013-09-19

Xueming Zhu 朱学明
Key Laboratory of Research on Marine Hazards Forecasting (LoMF), SOA
National Marine Environmental Forecasting Center (NMEFC)
No.8, Dahuisi Road, Haidian District, Beijing, 100081
People's Republic of China
Tel:+86-10-82481923

Comments on the Determination of Significance Levels
of the Coherence Statistic
Paul Julian
Journal of the Atmospheric Sciences, 1975
Volume 12, pp836-837

http://journals.ametsoc.org/doi/pdf/10.1175/1520-0469%281975%29032%3C0836%3ACOTDOS%3E2.0.CO%3B2

eg:
coh = .5
df = 6
p = 1.-(1.-coh)**(df/2.-1.)
print("p="+p)

On 9/18/13 8:54 AM, 朱学明 wrote:
> Hi Dennis,
> can you show me how does NCL caculate the spec@coher_probability?
> Thanks.
>
> 2013-09-18
>
>
>
> 朱学明
>
>
>
> 发件人：Dennis Shea <shea@ucar.edu>
> 发送时间：2013-09-18 07:29
> 主题：Re: [ncl-talk] confidence interval/level
> 收件人："朱学明"<557xiaozhu@163.com>
> 抄送："ncl-talk@ucar.edu USERS"<ncl-talk@ucar.edu>
>
> spec = specxy_anal(x,y,d,sm,pct)
> PHASE = spec@phase
> PHASE@_FillValue = 1e20
> PHASE = where(spec@coher_probability(1).le.0.95,PHASE@_FillValue,PHASE)
>
> =========
> See: http://www.ncl.ucar.edu/Applications/xy.shtml#ex25
>
> The right (R) plot should
>
>
> resR = True ; plot mods desired
> resR@xyMarkLineModes = "Markers" ; choose which have markers
> resR@xyMarkers = 16 ; choose type of marker
> resR@xyMarkerColor = "red" ; Marker color
> resR@xyMarkerSizeF = 0.005 ; Marker size (default 0.01)
>
>
> plot = gsn_csm_xy2(wks,spec@frq,spec@coher,PHASE,resL,resR)
>
>
> On 9/17/13 4:04 PM, 朱学明 wrote:
>> Hi all,
>> I have tried to use the function specxy_anal get the coherance and phase of two timeseries data based on the example script spec_2.ncl. But I just want to get the coherence and phase satisfy the 0.95 confidence level, the picture likes that in the attachment. How can I do that?
>> It looks like that the output of function specx_ci is not what I want.
>>
>> Any help would be appreciated. Thanks.
>>
>> 2013-09-18
>>
>>
>>
>> 朱学明
>>
>>
>>
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Received on Thu Sep 19 12:11:16 2013

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