linear interpolation functions in grads-2.0.a5.oga.5

James T. Potemra jimp at HAWAII.EDU
Wed Jul 15 19:38:49 EDT 2009


Hi Mike:

Thanks for the reply.  For some reason this causes my grads to exit.
I open the file, pick a point (lat,lon), then run trend=linreg(y) and
grads just quits (no error or seg fault):

              Welcome to the OpenGrADS Bundle Distribution
              --------------------------------------------

For additional information enter "opengrads --help".

Starting
"/usr/local/grads-2.0.a5.oga.5/Contents/Linux/Versions/2.0.a5.oga.5/x86_64/grads
-HC 1  -l -g 1000x800 " ...


Grid Analysis and Display System (GrADS) Version 2.0.a5.oga.5
Copyright (c) 1988-2008 by Brian Doty and the
Institute for Global Environment and Society (IGES)
GrADS comes with ABSOLUTELY NO WARRANTY
See file COPYRIGHT for more information

Config: v2.0.a5.oga.5 little-endian readline printim grib2 netcdf
hdf4-sds opendap-grids,stn athena geotiff
Issue 'q config' command for more information.
Loading User Defined Extensions table
</usr/local/grads-2.0.a5.oga.5/Contents/Linux/Versions/2.0.a5.oga.5/x86_64/gex/udxt>
... ok.
GX Package Initialization: Size = 11 8.5
Command line history in /export/lii/jimp/.grads.log
ga-> open c20c_tas
Scanning description file:  c20c_tas
Data file c20c_tas.nc is open as file 1
LON set to 0 360
LAT set to -89.4944 89.4944
LEV set to 1 1
Time values set: 1861:7:1:0 1861:7:1:0
E set to 1 1
ga-> set lat 0
LAT set to 1.01124 1.01124
ga-> set lon 180
LON set to 181.25 181.25
ga-> set t 1 140
Time values set: 1861:7:1:0 2000:7:1:0
ga-> d tas
ga-> trend=linreg(tas)


Michael Fiorino wrote:
> jim,
>
> my linreg extension does work...  e.g., trend=linreg(y)
>
> in a script the m and b are printed to the 'result' variable.
>
> /r mike
>
> James T. Potemra wrote:
>
>> I'm running grads-2.0.a5.oga.5 on a 64-bit linux machine and want to do
>> a linear
>> fit to a time-series.  There appears to be a UDF called "linreg" that is
>> included
>> in Mike Fiorino's UDF library, but the man page at
>> http://opengrads.org/doc/udxt/libmf/
>> does not list this function.
>>
>> Conversely, there is a man page for "tregr2" at
>> http://opengrads.org/doc/udxt/libbjt/
>> as part of Ben-Jei Tsuang's UDF library, but that does not appear in the
>> UDC list
>> (see list below).
>>
>> I would like to plot a linear fit through a time-series of a particular
>> variable.  It looks
>> like either of these would do this, but in my case the independent
>> variable is time, and
>> I'm not sure if I need to somehow define that in the Y = m * X + b
>> syntax for either
>> tregr2 or linreg.
>>
>> I'd appreciate any suggestions.  Thanks,
>>
>> Jim
>>
>> ------------------------------------------------------------------------------------------------------
>>
>>
>> ga-> q udf
>>
>>   User
>>  Defined
>>  FUNCTION          Short Description                Function at Library
>> ---------- -----------------------------------
>> --------------------------
>> lt         Less than operator                   f_bjt@^libbjt.gex
>> jd         Julian day                           f_bjt@^libbjt.gex
>> cosz       Cosine solar zenith angle            f_bjt@^libbjt.gex
>> dayratio   Daylight ratio                       f_bjt@^libbjt.gex
>> if         Conditional function                 f_bjt@^libbjt.gex
>> maxv       Maximum value                        f_bjt@^libbjt.gex
>> minv       Minimum value                        f_bjt@^libbjt.gex
>> which      Label gridpoints                     f_bjt@^libbjt.gex
>> ftest      F-test                               f_bjt@^libbjt.gex
>> ttest      T-test                               f_bjt@^libbjt.gex
>> tfit       Point  linear regression             f_bjt@^libbjt.gex
>> fit        Global linear regression             f_bjt@^libbjt.gex
>> tcorr2     Time correlation                     f_bjt@^libbjt.gex
>> tregr2     Point linear regression              f_bjt@^libbjt.gex
>> tmave2     Time averaging w/masking             f_bjt@^libbjt.gex
>> madvu      Calculates -d(u*EXPR)/dx             f_bjt@^libbjt.gex
>> madvv      Calculates -d(V*EXPR)/dy             f_bjt@^libbjt.gex
>> madvw      Calculates -d(W*EXPR)/dp             f_bjt@^libbjt.gex
>> muadv      Zonal advection                      f_bjt@^libbjt.gex
>> mvadv      Meridional advection                 f_bjt@^libbjt.gex
>> mwadv      Vertical advection                   f_bjt@^libbjt.gex
>> satvap     Saturated vapor pressure             f_bjt@^libbjt.gex
>> dew        Dew point temperature                f_bjt@^libbjt.gex
>> lw         Thermal infrared fluxes              f_bjt@^libbjt.gex
>> lw2        Thermal infrared fluxes v2           f_bjt@^libbjt.gex
>> pinterp    Pressure interpolation               f_bjt@^libbjt.gex
>> zinterp    Height interpolation                 f_bjt@^libbjt.gex
>> line       Draws a line                         f_bjt@^libbjt.gex
>> vint2      Mass-weighted vertical integral      f_bjt@^libbjt.gex
>> fish       Poisson solver                       f_fish@^fish.gex
>> fish_psi   Compute streamfunction               f_psichi@^fish.gex
>> fish_chi   Compute velocity potential           f_psichi@^fish.gex
>> fish_vor   Compute vorticity                    f_psichi@^fish.gex
>> fish_div   Compute divergence                   f_psichi@^fish.gex
>> dewpt      Dew-point temperature                f_gsudf@^gsudf.gex
>> ept        Equivalent potential temperature     f_gsudf@^gsudf.gex
>> epi        Potential Instability                f_gsudf@^gsudf.gex
>> plcl       Pressure at LCL                      f_gsudf@^gsudf.gex
>> shear      Wind Shear                           f_gsudf@^gsudf.gex
>> srh1km     Storm-relative Helicity 0-1km'       f_gsudf@^gsudf.gex
>> srh3km     Storm-relative Helicity 0-3km'       f_gsudf@^gsudf.gex
>> tlcl       Temperature at LCL                   f_gsudf@^gsudf.gex
>> tsindex    Chance of T-storm Initiation         f_gsudf@^gsudf.gex
>> ttindex    Total Totals Index                   f_gsudf@^gsudf.gex
>> wchill     Wind Chill Index (New)               f_gsudf@^gsudf.gex
>> hello      Hello, World! sample function        f_hello@^libhello.gex
>> ipc_save   Save expression to stream            f_Save@^libipc.gex
>> ipc_load   Load variable from file              f_Load@^libipc.gex
>> smth2d     Shuman smoother/de-smoother          f_smth2d@^libmf.gex
>> uv2trw     Find radial/tangential velocity      f_uv2trw@^libmf.gex
>> re2        General interpolator (regrid2)       f_re2@^libmf.gex
>> esmrf      Saturation vapor pressure (old MRF)  f_esmrf@^libmf.gex
>> linreg     Linear regression: mx + b            f_linreg@^libmf.gex
>> re         General interpolator                 ffre@^re.gex
>> re_        General interpolator (verbose)       ffre_dbg@^re.gex
>> regrid2    regrid2-like wrapper for re()        f_gsudf@^gsudf.gex
>> reimg      Interpolation for Image Generation'  f_gsudf@^gsudf.gex
>> sh_filt    Spherical harmonic filter            f_shfilt@^shfilt.gex
>> sh_power   Spherical harmonic spectra           f_shpowr@^shfilt.gex
>> ---------- -----------------------------------
>> --------------------------
>>



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