(As always, I hit "send" a moment too soon...)
That problem is a good example of the maxim that "when in doubt, add more
dimensions"... :-) Interpolators are particularly confusing because they have
to have a different number of active dims in different parameters/terms --
hence Chris's recent example, and the I-hope-now-well-known wart with index()
threading...
On Dec 9, 2013, at 9:44 AM, Craig DeForest <defor...@boulder.swri.edu> wrote:
> Hmmmm..
>
> If I understand right, you've enumerated the altitudes in lgrid and hgrid.
> Since you're interpolating over altitude, you want that moved to the pole
> position in the dim list in your $x and $y for your dplinear call.
> Everything else can be left alone. You want:
>
> * active dim: lgrid-altitude
> * thread dims: lat, lon, and hgrid-altitude
>
> After that, it's easy:
>
> $hg= Dutil::dplinear( $lgrid->mv(2,0), # (n: lo-alt, t0: lat, t1: lon)
> $t->mv(2,0), # (n: lo-alt, t0: lat, t1: lon)
> $hg # (t0: lat, t1: lon, t2: hi-alt)
> );
>
> I named the dimensions of each term, for clarity: 'n' is the active dim in
> the signature, the 't' dimensions are the thread dimensions. Note that $hg
> (the 'in()' term) is missing the active dim 'n', as the signature requires.
>
>
> On Dec 9, 2013, at 8:56 AM, Doug Hunt <dh...@ucar.edu> wrote:
>
>> Hi PDL folks: I just wrote a function that I think should be thread-able,
>> but I can't think how. Any ideas welcome.
>>
>> This function is used to up-sample a weather model grid via linear
>> interpolation. I use the local PP function Dutil::dplinear to do this. It
>> may be better to use other PDL interpolation functions, but I've been using
>> this for years and I know just what it does. Here is its signature:
>>
>> dplinear (x(n); y(n); in(); [o]out())
>>
>> It is just a simple interpolation routine which takes $x and $y vectors as
>> input, along with one value in $x-space to interpolate into $y space.
>>
>> The tricky bit here is that two sorts of threading are necessary:
>>
>> 1) Interpolating a column of input temperatures via the $x and $y input
>> to dplinear.
>>
>> 2) Threading over all the lat/lon columns in the input temperature grid $t.
>> The tricky bit is that the pressure values are different for each
>> column--this model does not use standard pressure levels, but the pressure
>> levels at each grid point depend upon the surface pressure.
>>
>> Any ideas? Please let me know if this is not clear...
>>
>> Regards,
>>
>> Doug Hunt
>>
>> --------------------------------------------------------------------------------------
>> sub upsampleGrid {
>>
>> my $lgrid = shift; # low resolution (half) pressure grid: lat x lon x 92
>> levels
>> my $hgrid = shift; # high resolution (half) pressure grid: lat x lon x 138
>> levels
>> my $t = shift; # temperature grid to upsample: lat x lon x level
>>
>> my ($nlat, $nlon, $llvl) = $t->dims; # llvl = 92
>> my $hlvl = ($hgrid->dims)[2]; # 138
>> my $ht = zeroes($nlat, $nlon, $hlvl); # high resolution output grid
>>
>> # This could be sped up with threading, I feel sure...
>> for (my $lati=0;$lati<$nlat;$lati++) {
>> for (my $loni=0;$loni<$nlon;$loni++) {
>> my $x = $lgrid->(($lati),($loni),:);
>> my $y = $t->(($lati),($loni),:);
>> my $in = $hgrid->(($lati),($loni),:);
>> $hg(($lati),($loni),:) .= Dutil::dplinear($x, $y, $in);
>> }
>> }
>>
>> return $hg;
>> }
>> --------------------------------------------------------------------------------------
>>
>> dh...@ucar.edu
>> Software Engineer
>> UCAR - COSMIC, Tel. (303) 497-2611
>>
>> _______________________________________________
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>> Perldl@jach.hawaii.edu
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>>
>
>
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