📄 gslib help postik.htm
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<H2>GSLIB Help Page: POSTIK</H2></CENTER>
<DL>
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<STRONG>Description:</STRONG>
<UL>
<LI>The output from <TT>ik3d</TT> requires additional processing before
being used. The program <TT>postik</TT> performs order relations
corrections, change of support calculations, and computes various statistics
according to the following options: </LI></UL>
<UL>
<LI>Compute the ``E-type'' estimate, i.e., the mean value of the conditional
distribution
<LI>Compute the variance the conditional distribution.
<LI>Compute the probability of exceeding a fixed threshold, the average
value above that threshold, and the average value below that threshold.
<LI>Compute the value where a fixed conditional cumulative distribution
function (cdf) value <I>p</I> is reached, i.e., the conditional
<I>p</I>-quantile value. </LI></UL>
<DT><IMG height=14 alt=o src="GSLIB Help POSTIK.files/ball.red.gif" width=14>
<STRONG>Parameters:</STRONG>
<UL>
<LI><B>distfl:</B> the output IK file (from program <TT>ik3d</TT>) which is
considered as input.
<LI><B>outfl:</B> the output file (output differs depending on output
option, see below).
<LI><B>iout</B> and <B>outpar:</B> <B>iout</B>=1 computes the E-type
estimate and the conditional variance, <B>iout</B>=2 computes the
probability and means above and below the value <B>outpar</B>, <B>iout</B>=3
computes the <I>z</I> value (<I>p</I>-quantile) corresponding to the cdf
value <B>outpar</B>=<I>p</I>, <B>iout</B>=4 computes the conditional
variance
<LI><B>ncut:</B> the number of thresholds.
<LI><B>cut(i),i=1,ncut:</B> the threshold values used in <TT>ik3d</TT>.
<LI><B>ivol, ivoltyp,</B> and <B>varred:</B> if <B>ivol</B> = 1 then volume
support correction is attempted with the affine correction
(<B>ivoltyp</B>=1) or the indirect correction through permanence of a
lognormal distribution (<B>ivoltyp</B>=2). The variance reduction factor
(between 0 and 1) is specified as <B>varred</B>.
<LI><B>datafl:</B> the data file containing <I>z</I>-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 options.
<LI><B>icolvr</B> and <B>icolwt:</B> when either <B>ltail, middle</B> or
<B>utail</B> is 3 then these variables identify the column for the values
and the column for the (declustering) weight in <B>datafl</B> that will be
used for the global distribution.
<LI><B>tmin</B> and <B>tmax:</B> all values strictly less than <B>tmin</B>
and strictly greater than <B>tmax</B> are ignored.
<LI><B>zmin</B> and <B>zmax:</B> 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 <B>zmax</B>.
<LI><B>ltail</B> and <B>ltpar</B> specify the extrapolation in the lower
tail: <B>ltail</B>=1 implements linear interpolation to the lower limit
<B>zmin</B>; <B>ltail</B>=2 implements power model interpolation, with
<B>w=ltpar</B>, to the lower limit <B>zmin</B>; and <B>ltail</B>=3
implements linear interpolation between tabulated quantiles.
<LI><B>middle</B> and <B>midpar</B> specify the interpolation within the
middle of the distribution: <B>middle</B>=1 implements linear interpolation
to the lower limit <B>zmin</B>; <B>middle</B>=2 implements power model
interpolation, with <B>w=midpar</B>, to the lower limit <B>zmin</B>; and
<B>middle</B>=3 allows for linear interpolation between tabulated quantile
values.
<LI><B>utail</B> and <B>utpar</B> specify the extrapolation in the upper
tail of the distribution: <B>utail</B>=1 implements linear interpolation to
the upper limit <B>zmax</B>, <B>utail</B>=2 implements power model
interpolation, with <B>w=utpar</B>, to the upper limit <B>zmax</B>;
<B>utail</B>=3 implements linear interpolation between tabulated quantiles;
and, <B>utail</B>=4 implements hyperbolic model extrapolation with
<B>w=utpar</B>.
<LI><B>maxdis:</B> 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 </LI></UL>
<DT><IMG height=14 alt=o src="GSLIB Help POSTIK.files/ball.red.gif" width=14>
<STRONG>Application notes:</STRONG>
<UL>
<LI>Although order relations are corrected by <TT>ik3d</TT> they are checked
again in <TT>postik</TT>.
<LI>A facility for volume support correction has been provided although we
<B>strongly</B> suggest that volume support correction be approached through
small-scale simulations. Either the affine correction or the indirect
lognormal correction is available.
<LI>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.
<LI>Both the conditional (E-type) mean and the mean above a specified
threshold are calculated by summing the <I>z</I> values at regularly spaced
ccdf increments. A parameter <B>maxdis</B> specifies how many such cdf
values to calculate. This can be increased depending on the precision
required. </LI></UL></DT></DL><IMG height=8 alt=---
src="GSLIB Help POSTIK.files/line.blue.gif" width=652>
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