GSLIB Help Page: POSTIK
The output from ik3d requires additional processing before
being used. The program postik performs order relations
corrections, change of support calculations, and computes various
statistics according to the following options:
Compute the ``E-type'' estimate, i.e., the mean value
of the conditional distribution
Compute the variance the conditional distribution.
Compute the probability of exceeding a fixed threshold, the average
value above that threshold, and the average value below that threshold.
Compute the value where a fixed conditional cumulative distribution
function (cdf) value p is reached, i.e., the conditional
distfl: the output IK file (from program ik3d) which is
considered as input.
outfl: the output file (output differs depending on output
option, see below).
iout and outpar: iout=1 computes the E-type
estimate and the conditional variance, iout=2 computes the
probability and means above and below the value outpar,
iout=3 computes the z value (p-quantile)
corresponding to the cdf value outpar=p, iout=4
computes the conditional variance
ncut: the number of thresholds.
cut(i),i=1,ncut: the threshold values used in ik3d.
ivol, ivoltyp, and varred: if ivol = 1 then volume
support correction is attempted with the affine correction
(ivoltyp=1) or the indirect correction through permanence of a
lognormal distribution (ivoltyp=2). The variance reduction
factor (between 0 and 1) is specified as varred.
datafl: the data file containing z-data that provides the
details between the IK thresholds. This file is used only if table
look-up values are called for in one of the interpolation/extrapolation
icolvr and icolwt: when either
ltail, middle or utail is 3 then these variables identify
the column for the values and the column for the (declustering) weight
in datafl that will be used for the global distribution.
tmin and tmax: all values strictly less than tmin
and strictly greater than tmax are ignored.
zmin and zmax: minimum and maximum data values allowed.
Even when not using linear interpolation it is safe to control
the minimum and maximum values entered. The lognormal or
hyperbolic upper tail is constrained by zmax.
ltail and ltpar specify the extrapolation in the lower
tail: ltail=1 implements linear interpolation to the lower limit
zmin; ltail=2 implements power model interpolation, with
w=ltpar, to the lower limit zmin; and
ltail=3 implements linear interpolation between tabulated
middle and midpar specify the interpolation within the
middle of the distribution: middle=1 implements linear
interpolation to the lower limit zmin; middle=2 implements
power model interpolation, with w=midpar, to the lower
limit zmin; and middle=3 allows for linear interpolation
between tabulated quantile values.
utail and utpar specify the extrapolation in the upper
tail of the distribution: utail=1 implements linear interpolation
to the upper limit zmax, utail=2 implements power model
interpolation, with w=utpar, to the upper limit
zmax; utail=3 implements linear interpolation between
tabulated quantiles; and, utail=4 implements hyperbolic model
extrapolation with w=utpar.
maxdis: a maximum discretization parameter. The default value
of 50 is typically fine; greater accuracy is obtained with a larger
number and quicker execution time is obtained with a lower number.
A short description of the program
Although order relations are corrected by ik3d they are
checked again in postik.
A facility for volume support correction has been provided although
we strongly suggest that volume support correction be
approached through small-scale simulations. Either the affine
correction or the indirect lognormal correction is available.
There are a number of consequential decisions that must be made about
how to interpolate between and extrapolate beyond known values of the
cumulative distribution function.
Both the conditional (E-type) mean and the mean above a specified
threshold are calculated by summing the z values at regularly
spaced ccdf increments. A parameter maxdis specifies how many
such cdf values to calculate. This can be increased depending on the