Re: How to fit data with a straight line

[Yang Haijun <navyang@xxxxxxxxxxxxxxxxxxxx>]

Hi, Steve,

Thank you very much.

As you said, I define axis like this

  yes? def axis/t=1-jan-1945:31-dec-1993:365.25/units=days/edges tax1
  yes? tmean=temp[gt=tax1@ave]
  
 instead of 
 
  yes? def axis/t=1-jan-1945:31-dec-1993:365.25/units=days/edges/modulo tax1
  yes? tmean=temp[gt=tax1@mod]
 
 Then I use regresst
 
  yes? let q = tmean
  yes? let p = t[gt=tax1]
  yes? go regresst
  
 and plot line
 
  yes? plot/x=180/y=20 tmean
  yes? plot/x=180/y=20/over qhat
  
 they work very well and I get what I want.
 
 But here I have two problems more, 
 
 1) you must notice here I do not use
 
  yes? set grid q
  
  If I use this line, then I would be pushed out of ferret,

  yes? set grid q
  yes? go regresst
  yes? plot/x=180/y=20 qhat  
  Segmentation fault (core dumped)
  
 2) My data is 3 Dimensional, when I do 
 
  yes? contour qhat[l=20]
**ERROR: all data have same value: data are all flagged as bad
  
  I get error. But when I list data 'qhat'
  
  yes? list qhat
  
  qhat has value on every point and every time step
  
  If I list qhat like this,
  
  yes? list/l=20 qhat
               SLOPE*P + INTERCEP
             TIME: 02-JUL-1964 09:00
      ... listing every   3th point
           179E175W169W163W157W151W145W139W133W127W121W115W109W103W97W 91W 85W 79W 
           41  44  47  50  53  56  59  62  65  68  71  74  77  80  83  86  89  92
61N / 52:.........................................................................
59N / 51:.........................................................................
 ...
 
  Now no values at all. I do not understand.
  
  So I draw contour like,
  
  yes? contour qhat[l=20:21@ave]
  
  I can get very good contours, just what I want. I am curious to get these problems.
  
 Thanks a lot.

Haijun Yang
 
 

 
  
  
> From hankin@pmel.noaa.gov Thu Mar 23 15:24:52 2000
> Date: Thu, 23 Mar 2000 13:38:25 -0800
> From: Steve Hankin <hankin@pmel.noaa.gov>
> Subject: Re: How to fit data with a straight line
> To: Yang Haijun <navyang@tuna.meteor.wisc.edu>
> Cc: ferret_users@ferret.wrc.noaa.gov, verschell@neptune.gsfc.nasa.gov
> Organization: NOAA/Pacific Marine Environmental Laboratory
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> Content-Type: multipart/mixed; boundary="Boundary_(ID_pz8DKlw3VXY9Jm0qKRjiRQ)"
> X-Accept-Language: en
> References: <200003230002.AA15416@tuna.meteor.wisc.edu>
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> 
> Hi Yang,
> 
> First I see a couple of more fundamental problems.
> 
>   1. The axis TAX is an year-by-year (non-modulo) axis. You have included a "modulo"
>      qualifier, but I think it does not belong there.
>   2. You have also asked for TEMP[gt=tax1@mod], modulo regridding. I believe what you
>      want is simple TEMP[gt=tax1@AVE] -- to average the (monthly) source points into
>      the (annual) destination cells.
> 
> Here is a complete session illustrating the type of calculation that you are
> attempting. I use a SIN function for synthetic data. The resulting GIF file is
> attached.
> 
>      yes? define axis/t=1-jan-1945:31-dec-1993:30/units=days tsrc
>      yes? let my_var = SIN(T[gt=tsrc]/500)
>      yes? plot my_var
>      yes? def axis/t=1-jan-1945:31-dec-1993:365.25/units=days/edges tax1
>      yes? let my_var_ann = my_var[gt=tax1@ave]
>      yes? plot/over/symbols my_var_ann
>      yes? go regresst
> 
>           ... Linear Regression Along the T Axis
>           ... Instructions:
>           Use the LET command to define new variables
>           Define the variable P as your independent (X) variable
>           Define the variable Q as your   dependent (Y) variable
>           Results will be variables "SLOPE", "INTERCEP" and "RSQUARE"
>           QHAT will be the regression estimate
>           Note: If "T" is your independent variable then
>           ...   "SET GRID Q" after defining Q.
>           ...
> 
>      yes? let p = t[gt=tax1]
>      yes? let q = my_var_ann
>      yes? plot/over qhat
>      yes? frame/file=qhat.gif
> 
>     Happy Ferreting - steve
> 
> ================================================
> 
> Yang Haijun wrote:
> 
> > 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>
> > > X-Mailer: Z-Mail (5.0.0 30July97)
> > > To: Yang Haijun <navyang@tuna.meteor.wisc.edu>,
> >         ferret_users@ferret.wrc.noaa.gov
> > > Subject: Re: How to fit data with a straight line
> > > Mime-Version: 1.0
> > > Content-Type: text/plain; charset=us-ascii
> > > Sender: owner-ferret_users@ferret.wrc.noaa.gov
> > > Precedence: bulk
> > > Content-Length: 872
> > >
> > > 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
> > >
> > >
> > >
> 
> --
> 
>                 |  NOAA/PMEL               |  ph. (206) 526-6080
> Steve Hankin    |  7600 Sand Point Way NE  |  FAX (206) 526-6744
>                 |  Seattle, WA 98115-0070  |  hankin@pmel.noaa.gov
> 
>