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Re: [ferret_users] error in calculating correlation coefficient



Thanks Mick. It worked. But, this apparently also works and gave the same value of correlation coefficient.

def axis/t=1:17:1 tax ; def grid/t=tax grd
let p=hci[d=1,gt=grd@asn] ; let q=j4pranom2[d=2,gt=grd@asn]

as well as this:

def axis/t=1:17:1 tax
let p=hci[d=1,gt=tax@asn] ; let q=j4pranom2[d=2,gt=tax@asn]

I am asuming they are equivalent in this context.
 
Jagadish

From: mick spillane <Mick.Spillane@xxxxxxxx>
To: jagadish karmacharya <j_karmacharya@xxxxxxxxx>
Sent: Friday, August 5, 2011 9:13 PM
Subject: Re: [ferret_users] error in calculating correlation coefficient

Hi Jagadish,
    Here is something you might try.

def axis/t=1:17:1 tax ; def grid/t=tax grd
let p=hci[d=1,g=grd,gt=@asn]
let q=j4pranom2[d=2,g=grd,gt=@asn]
list p,q

The regridding you did before probably linearly interpolated the one
variable onto the time axis of the other -- hence the change in the
"raw" data. Using the
@asn transformation each original series is transferred one-to-one onto
an axis 1,2,...,17 so "list p,q" should return the values you expect and
you can then continue with the correlation.

Hope this helps,
    Mick
-------
On 8/5/11 12:16 PM, jagadish karmacharya wrote:
> Dear ferret users.
>
> I want to calculate temporal correlation between two datasets. Both datasets are area average values with equal number of time steps but ferret is giving error when I tried to compute correlation between the two. My guess is there is inconsistency in unit of time dimension between the dataset which is causing the problem. But how can I overcome this?
> ==========
> Below is my commands and ferret messages:
>
> use HCIyear17.nc, j4pranom2.nc
> sh d/f
>      currently SET data sets:
>      1>  ./HCIyear17.nc
>  name    title                            I        J       
>  K        L
>  HCI      V850ANOM-V200ANOM                1:1      1:1      1:1      1:17
>                on grid GTL1 with -1.000000E+34 for missing data
>              X=90.2E:91.2E  Y=19.8N:20.8N  Z=849.5:850.5
>    time range: 15-SEP-1989 21:00 to 15-SEP-2005 21:00
>
>      2>  ./j4pranom2.nc  (default)
>  name    title                           
>  I        J        K        L
>  J4PRANOM2
>            PRECIP[D=3]-J4PRCLM2            ...      ...      ...      1:17
>        (X=70E:90E@AV4, Y=6.2N:25N@AV4)
>                on grid GPA1 with -1.000000E+34 for missing data
>    time range: 30-SEP-1989 00:00 to 30-SEP-2005 00:00
>
> let p=hci[d=1]; let q=j4pranom2[d=2]
> go variance
> ...
> list correl
> ...
>  **ERROR: illegal limits: Q is not in the range T=04-JAN-1971 03:22:19-SEP-1971 20:22
>            Axis extremes are T=31-MAR-1989 12:00:31-MAR-2006 12:00
>    =========
>
> Then I found from the mailing archieve that the one variables can be regridded to the
> other grid, with a regridding transformation. I tried that
> and apparently it worked but upon close inspection I found that during
> transfermation the values differs from the original and  one value at
> the edge was flagged as bad so my guess is this will affect the correlation
> computated.This is what I mean: continuing from above
>
> stat j4pranom2
>              PRECIP[D=3]-J4PRCLM2
>              X=70E:90E@AV4, Y=6.2N:25N@AV4
>              X:  N/A
>              Y:  N/A
>              Z:  N/A
>              TIME: 31-MAR-1989 12:00 to 31-MAR-2006 12:00
>              DATA SET: ./j4pranom2.nc
>  Total # of data points: 17 (1*1*1*17)
>  # flagged as bad  data: 0
>  Minimum value:
>  -1.722
>  Maximum value: 4.0644
>  Mean    value: 0.00030241 (unweighted average)
>  Standard deviation: 1.2375
>
> let q=j4pranom2[d=2,gt=p]
> stat q
>              J4PRANOM2[D=j4pranom2,GT=P]
>              X:  N/A
>              Y:  N/A
>              Z:  N/A
>              TIME: 17-MAR-1989 09:00 to 17-MAR-2006 09:00
>              DATA SET: N/A
>  Total # of data points: 17
>  (1*1*1*17)
>  # flagged as bad  data: 1
>  Minimum value: -1.6715
>  Maximum value: 3.8625
>  Mean    value: -0.0095812 (unweighted average)
>  Standard deviation: 1.2196
>
> ============
>
> I look forward to your advice.
>
> Best regards,
> Jagadish
>
> =====
> Below is the ncdump output of the files:
>
> ncdump -h HCIyear17.nc
>
> netcdf HCIyear17 {
> dimensions:
>          LON = 1 ;
>          LAT = 1 ;
>          LEV2_2 = 1 ;
>          TIME = UNLIMITED ; // (17 currently)
>          bnds = 2 ;
> variables:
>          double LON(LON) ;
>                  LON:units = "degrees_east"
>  ;
>                  LON:modulo = 360. ;
>                  LON:point_spacing = "even" ;
>                  LON:axis = "X" ;
>          double LAT(LAT) ;
>                  LAT:units = "degrees_north" ;
>                  LAT:point_spacing = "even" ;
>                  LAT:axis = "Y" ;
>          double LEV2_2(LEV2_2) ;
>                  LEV2_2:units = "Pa"
>  ;
>                  LEV2_2:point_spacing = "even" ;
>                  LEV2_2:axis = "Z" ;
>          double TIME(TIME) ;
>                  TIME:units = "days since 1989-01-01 00:00:00" ;
>                  TIME:time_origin = "01-JAN-1989 00:00:00" ;
>                  TIME:axis = "T" ;
>                  TIME:bounds = "TIME_bnds" ;
>          double TIME_bnds(TIME, bnds) ;
>          float HCI(TIME,
>  LEV2_2, LAT, LON) ;
>                  HCI:missing_value = -1.e+34f ;
>                  HCI:_FillValue = -1.e+34f ;
>                  HCI:long_name = "V850ANOM-V200ANOM" ;
>                  HCI:history = "From HCI" ;
> // global attributes:
>                  :history = "FERRET V6.5    5-Aug-11" ;
>                  :Conventions = "CF-1.0" ;
>
> ncdump -h j4pranom2.nc
>
> netcdf j4pranom2 {
> dimensions:
>      TIME = UNLIMITED ; // (17 currently)
>      bnds = 2 ;
> variables:
>      double TIME(TIME) ;
>          TIME:units = "hours since 1971-01-01 00:00:00" ;
>          TIME:time_origin = "01-JAN-1971 00:00:00" ;
>          TIME:axis = "T" ;
>          TIME:bounds = "TIME_bnds" ;
>      double TIME_bnds(TIME, bnds) ;
>      float J4PRANOM2(TIME) ;
>          J4PRANOM2:missing_value = -1.e+34f ;
>          J4PRANOM2:_FillValue = -1.e+34f
>  ;
>          J4PRANOM2:long_name = "PRECIP[D=3]-J4PRCLM2" ;
>          J4PRANOM2:long_name_mod = "X=70E:90E@AV4, Y=6.2N:25N@AV4" ;
>
> // global attributes:
>          :history = "FERRET V6.5    5-Aug-11" ;
>          :Conventions = "CF-1.0" ;
> }
>




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