ncflint - Online in the Cloud

PROGRAM:

NAME

ncflint - netCDF File Interpolator

SYNTAX

ncflint [-3] [-4] [-6] [-7] [-A] [--bfr sz][-C][-c][--cnk_byt sz][--cnk_dmn nm,sz]
[--cnk_map map] [--cnk_min sz] [--cnk_plc plc] [--cnk_scl sz][-D dbg_lvl] [-d dim,[
min][,[ max]]] [-F] [--fix_rec_crd] [-G gpe_dsc] [-g grp[,...]] [--glb att_name=
att_val]] [-h] [--hdf] [--hdr_pad sz] [-i var,val3][-L dfl_lvl][-l path] [--msa]
[--no_tmp_fl] [-O] [-p path] [--ppc var1[, var2[,...]]= prc]] [-R] [-r] [--ram_all] [-t
thr_nbr] [--unn] [-v var[,...]] [-w wgt[, wgt2]] [-X box] [-x] file1 file2 file3

DESCRIPTION

ncflint creates an output file that is a linear combination of the input files. This
linear combination can be a weighted average, a normalized weighted average, or an
interpolation of the input files. Coordinate variables are not acted upon in any case,
they are simply copied from file_1.
There are two conceptually distinct methods of using ncflint. The first method is to
specify the weight each input file is to have in the output file. In this method, the
value val3 of a variable in the output file file_3 is determined from its values val1 and
val2 in the two input files according to wgt1*val1+wgt2*val2

Here at least wgt1, and, optionally, wgt2, are specified on the command line with the -w
(or --weight or --wgt_var ) switch. If only wgt1 is specified then wgt2 is automatically
computed as wgt2=1-wgt1. Note that weights larger than 1 are allowed. Thus it is
possible to specify wgt1=2 and wgt2=-3. One can use this functionality to multiply all
the values in a given file by a constant.

The second method of using ncflint is to specify the interpolation option with -i (or with
the --ntp or --interpolate long options). This is really the inverse of the first method
in the following sense. When the user specifies the weights directly, ncflint has no work
to do besides multiplying the input values by their respective weights and adding the
results together to produce the output values. This assumes it is the weights that are
known a priori. In another class of cases it is the "arrival value" (i.e., val3 ) of a
particular variable var that is known a priori. In this case, the implied weights can
always be inferred by examining the values of var in the input files. This results in one
equation in two unknowns, wgt1 and wgt2: val3=wgt1*val1+wgt2*val2.

Unique determination of the weights requires imposing the additional constraint of
normalization on the weights: wgt1+wgt2=1. Thus, to use the interpolation option, the
user specifies var and val3 with the -i option. ncflint will compute wgt1 and wgt2, and
use these weights on all variables to generate the output file. Although var may have any
number of dimensions in the input files, it must represent a single, scalar value. Thus
any dimensions associated with var must be "degenerate", i.e., of size one.

If neither -i nor -w is specified on the command line, ncflint defaults to weighting each
input file equally in the output file. This is equivalent to specifying -w 0.5 or -w
0.5,0.5. Attempting to specify both -i and -w methods in the same command is an error.

ncflint is programmed not to interpolate variables of type NC_CHAR and NC_BYTE. This
behavior is hardcoded.

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