Re: How to fit data with a straight line

[Yang Haijun <navyang@xxxxxxxxxxxxxxxxxxxx>]

Hi,

  Thank you very much. Bu now I have another problem,

  Suppose I have data temperature with 49 year x 12 months = 588 time steps
  
 currently SET data sets:
    1> temp.nc  (default)
 name     title                             I         J         K         L
 TEMP     COADS SST                        1:97      1:57      ...       1:588
 PERIOD   Averaging period                 ...       ...       ...       1:588

1)  First of all I get annual mean temp
  
  yes? def axis/t=1-jan-1945:31-dec-1993:365.25/units=days/edges/modulo tax1
  yes? let TMEAN = TEMP[gt=tax1@mod]

2)  Then I want to do regress for TMEAN  

  yes? let q = TMEAN
  yes? let p = t
  yes? set grid TMEAN
  yes? go regresst
  
Then I got error messages:
  
 **ERROR: unknown defining grid: GT=TAX1@MOD --> g=user-or-pseudo-var not allowed
 set grid TMEAN
 Command file, command group, or REPEAT execution aborted
 
 Obviously the problem is due to 't', how to give 't' to p here?
 And let ferret know this 't' is corresponding to TMEAN?
 
 Thanks a lot.
 
 
Haijun Yang 
 

  

> From ferret_users-owner@ferret.wrc.noaa.gov Wed Mar 22 15:00:35 2000
> From: "Mark Verschell" <verschell@neptune.gsfc.nasa.gov>
> Date: Wed, 22 Mar 2000 15:45:57 -0500
> In-Reply-To: Yang Haijun <navyang@tuna.meteor.wisc.edu>
        "How to fit data with a straight line" (Mar 22,  1:48pm)
> References: <200003221948.AA14779@tuna.meteor.wisc.edu>
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> To: Yang Haijun <navyang@tuna.meteor.wisc.edu>,
        ferret_users@ferret.wrc.noaa.gov
> Subject: Re: How to fit data with a straight line
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> 
> Look at the .jnl files regress?.jnl that would be in $FER_DIR/go, since you are
> trying to do this versus time, you would use regresst.jnl. A simple example for
> your case:
> 
> yes? let p=temperature
> yes? let q=t
> yes? set grid q
> yes? go regresst
> 
> Then:
> 
> yes? list slope, intercep, rsquare ! slope is b and intercep is a
> 
> You can also plot this with
> 
> yes? plot qhat
> 
> Mark
> 
> On Mar 22,  1:48pm, Yang Haijun wrote:
> > Subject: How to fit data with a straight line
> > Dear ferret users,
> >
> > I have a time-series data, say Temperature with 40 years, now I want to fit
> this data with a
> > straight line, that is, I want to get this line:
> >
> >   Y = a + b*t
> >
> >  based on Temperature observations. Here Y is temperature, t is time step.
> How do I get 'a' and
> > 'b'? Is there a function to do this in ferret?
> >
> >  Thank you very much,
> >
> >  Haijun Yang
> >-- End of excerpt from Yang Haijun
> 
> 
>