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

[Cristian Gonzal Muñoz Castillo]

I think most of us agree that grads is not so suitable when we want to
make some calculations (e.g. regressions). What i would do is just fit the
linear regression to the data using matlab or any other software. It is
not difficult to translate the results to a readable ctl file for grads.

I hope this works for you, regards

> 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
>  ---------- -----------------------------------
> --------------------------
>


--
Cristian G. Muñoz Castillo
Licenciado en Ciencias Físicas
Candidato a Geofísico
Of. 442
Tel. (41) 2203155
Depto. Geofísica
Facultad Ciencias Físicas y Matemáticas
Universidad de Concepción
Concepción
Chile
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