Re: Need a help for a logic of escorc

From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>
Date: Wed Aug 14 2013 - 09:33:58 MDT

Please do not send me direct emails. I have my own job to do. THX.

===

Alessandra's response was "appropriate". However, another approach
may be the following where *you* 'manually' do the lag operation.

Note: escorc requires that the number of time steps be the same.

Something like the following.

   X = (time,lat,lon)
   Y = (time,lat,lon)

undef("erika_lag")
function erika_lag(X[*][*][*], Y[*][*][*], mxlag[1]:integer)
begin
   x = X(lat|:,lon|:,time|:)
   y = Y(lat|:,lon|:,time|:)

   dimx = dimsizes(x)
   nlat = dimx(0)
   mlon = dimx(1)
   ntim = dimx(2)
   ntim1 = ntim-1 ; convenience

   mxlag = 15
   r = new ( (/2*mxlag+1,nlat,mlon/), typeof(x), getFillValue(x))

   r(mxlag+1,:,:) = escorc(x,y) ; correlation at lag 0

   do m=1,mxlag ; x lead y
      myStrt = m
      myLast = ntim1
      r(mxlag+1+m,:,:) = escorc(x(:,:,0:ntim1-m),y(:,:,myStrt:myLast))
   end do

   do m=1,mxlag ; y lead x
      myStrt = ?
      myLast = ?
      r(m-mxlag-1,:,:) = escorc(y(:,:,myStrt:myLast)), x(:,:,0:ntim1-m))
   end do

   r!0 = "lag"
   r&lag = ispan(-mxlag,mxlag,1) ; -15 to 15
   copy_VarCoords(x(:,:,0), r(0,:,:))
   printVarSummary(r)

   return(r)
end

On 8/14/13 6:01 AM, Erika Folova wrote:
> Dear NCL Team,
>
> It was posted a week ago but havenít got any appropriate response yet -(
> I am begging a suggestion for this tricky problem.
>
> Actually the question is how can I* control the date* for Y. For X is OK to
> keep it *fixed 90 days* for each year from 1 January to 30 March. But for Y
> is quite hard for me to understand how can I shift it by -15 to 15 days
> relative to X, meaning that Y time series start on 17 December and 15
> January for the first and the last analysis.
>
> Here is the illustration of the setting of time series :
>
> lag 0: X: 1 Jan |----------------------| 31 Mar 1
> Jan|----------------------|31 Mar .....
> Y: 1 Jan |----------------------| 31 Mar 1
> Jan|----------------------|31 Mar .....
>
> lag -1 X: 1 Jan |----------------------| 31 Mar 1
> Jan|----------------------|31 Mar ....
> Y: 31 Dec |----------------------| 30 Mar 31
> Dec|----------------------|30 Mar ....
>
> lag +1 X: 1 Jan |----------------------| 31 Mar 1
> Jan|----------------------|31 Mar ....
> 2 Jan |----------------------| 1 Apr 2
> Jan|----------------------| 1 Apr ....
>
>
> Thank you so much for your kind suggestion,
> It means a lot for me to figure out this matter.
> Thank you
>
> Best,
> Erika
>
>
>
>
>
>
> On Fri, Aug 9, 2013 at 8:54 PM, Erika Folova <e.folova@gmail.com> wrote:
>> I meant as I described earlier, I want to keep 90-day time period for X
>> "fixed" from1 January to 31 March while the time series of the Y is
> shifted
>> by -15 to 15 days (nlag= +/- 15 ). That meansthe Y time series start on 17
>> December and 15 January for the first and the last analysis. I still do
> not
>> have an idea how to make it easily. Any help will be really appreciated.
>>
>> Thank you,..
>>
>>
>>
>>
>> On Fri, Aug 9, 2013 at 2:42 AM, Alessandra Giannini
>> <alesall@iri.columbia.edu> wrote:
>>>
>>>
>>> Hi Erika,
>>>
>>> NCL has a correlation function that allows for lags:
>>>
>>> <http://www.ncl.ucar.edu/Document/Functions/Built-in/esccr.shtml>
>>>
>>> cheers, alessandra
>>>
>>>
>>>
>>>
>>>
>>> On Aug 8, 2013, at 1:38 PM, Erika Folova <e.folova@gmail.com> wrote:
>>>
>>> So.. no suggestion for my case :-(
>>>
>>>
>>> On Sat, Jul 27, 2013 at 5:58 AM, Erika Folova <e.folova@gmail.com> wrote:
>>>>
>>>> Hallo NCL,
>>>>
>>>> Lately I am quite confused to set my code to do a cross correlation,
>>>> The role is as follows: I have daily datasets lets say X and Y
>>>> extending for 5 years. The role is, I want to keep 90-day time period
> for
>>>> X "fixed" from
>>>> 1 January to 31 March while the time series of the Y is shifted by -15
> to
>>>> 15 days (nlag= +/- 15 ). That means
>>>> the Y time series start on 17 December and 15 January for the first and
>>>> the last analysis.
>>>>
>>>> What I think is something like this:
>>>>
>>>> mxlag = 15
>>>> lag = ispan(-mxlag,mxlag,1)
>>>>
>>>> do l = -mxlag,mxlag
>>>> CC (l+mxlag,:) = escorc( X(time), Y(time|time+l))
>>>> end do
>>>>
>>>> But I guess this is a wrong approach because I just want to concern on
>>>> JFM fixed on X but shifted for Y as I mentioned previously,
>>>> Any help would be really appreciated.
>>>>
>>>> Thank you
>>>>
>>>> Erika,
>>>
>>>
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>>>
>>
>
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Received on Wed Aug 14 09:33:36 2013

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