📄 gslib help sgsim.htm
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<H2>GSLIB Help Page: SGSIM</H2></CENTER>
<DL>
<DT><IMG height=14 alt=o src="GSLIB Help SGSIM.files/ball.red.gif" width=14>
<STRONG>Description:</STRONG>
<UL>
<LI>Sequential Gaussian simulation program </LI></UL>
<DT><IMG height=14 alt=o src="GSLIB Help SGSIM.files/ball.red.gif" width=14>
<STRONG>Parameters:</STRONG>
<UL>
<LI><B>datafl:</B> the input data in a simplified Geo-EAS formatted file. If
this file does not exist then an unconditional simulation will be generated.
<LI><B>icolx, icoly, icolvr, icolwt</B> and <B>icolsec:</B> the column
numbers for the <I>x,y</I> and <I>z</I> coordinates, the variable to be
simulated, the declustering weight, and the secondary variable (e.g., for
external drift if used). One or two of the coordinate column numbers can be
set to zero which indicates that the simulation is 2-D or 1-D. For equal
weighting, set <B>icolwt</B> to zero.
<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>itrans:</B> if set to 0 then no transformation will be performed; the
variable is assumed already standard normal (the simulation results will
also be left unchanged). If <B>itrans=1</B>, transformations are performed.
<LI><B>transfl:</B> output file for the transformation table if
transformation is required (<B>igauss</B>=0).
<LI><B>ismooth:</B> if set to 0, then the data histogram, possibly with
declustering weights is used for transformation, if set to 1, then the data
are transformed according to the values in another file (perhaps from
histogram smoothing).
<LI><B>smthfl:</B> file with the values to use for transformation to normal
scores (if <B>ismooth</B> is set to 0).
<LI><B>icolvr</B> and <B>icolwt:</B> columns in <B>smthfl</B> for the
variable and the declustering weight (set to 1 and 2 if <B>smthfl</B> is the
output from <TT>histsmth</TT>).
<LI><B>zmin</B> and <B>zmax</B> the minimum and maximum allowable data
values. These are used in the back transformation procedure.
<LI><B>ltail</B> and <B>ltpar</B> specify the back transformation
implementation in the lower tail of the distribution: <B>ltail</B>=1
implements linear interpolation to the lower limit <B>zmin</B>, and
<B>ltail</B>=2 implements power model interpolation, with <B>w=ltpar</B>, to
the lower limit <B>zmin</B>.
<LI>The middle class interpolation is linear.
<LI><B>utail</B> and <B>utpar</B> specify the back transformation
implementation 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>, and <B>utail</B>=4 implements hyperbolic model
extrapolation with <B>w=utpar</B>. The hyperbolic tail extrapolation is
limited by <B>zmax</B>.
<LI><B>idbg:</B> an integer debugging level between 0 and 3. The larger the
debugging level the more information written out.
<LI><B>dbgfl:</B> the file for the debugging output.
<LI><B>outfl:</B> the output grid is written to this file. The output file
will contain the results, cycling fastest on <I>x</I> then <I>y</I> then
<I>z</I> then simulation by simulation.
<LI><B>nsim:</B> the number of simulations to generate.
<LI><B>nx, xmn, xsiz:</B> definition of the grid system (<I>x</I> axis).
<LI><B>ny, ymn, ysiz:</B> definition of the grid system (<I>y</I> axis).
<LI><B>nz, zmn, zsiz:</B> definition of the grid system (<I>z</I> axis).
<LI><B>seed:</B> random number seed (a large odd integer).
<LI><B>ndmin</B> and <B>ndmax:</B> the minimum and maximum number of
original data that should be used to simulate a grid node. If there are
fewer than <B>ndmin</B> data points the node is not simulated.
<LI><B>ncnode:</B> the maximum number of previously simulated nodes to use
for the simulation of another node.
<LI><B>sstrat:</B> if set to 0, the data and previously simulated grid nodes
are searched separately: the data are searched with a super block search and
the previously simulated nodes are searched with a spiral search (see
section II.4). If set to 1, the data are relocated to grid nodes and a
spiral search is used and the parameters <B>ndmin</B> and <B>ndmax</B> are
not considered.
<LI><B>multgrid:</B> a multiple grid simulation will be performed if this is
set to 1 (otherwise a standard spiral search for previously simulated nodes
is considered).
<LI><B>nmult:</B> the number of multiple grid refinements to consider (used
only if <B>multgrid</B> is set to 1).
<LI><B>noct:</B> the number of original data to use per octant. If this
parameter is set less than or equal to 0, then it is not used; otherwise, it
overrides the <B>ndmax</B> parameter and the data is partitioned into
octants and the closest <B>noct</B> data in each octant is retained for the
simulation of a grid node.
<LI><B>radius_hmax</B>, <B>radius_hmin</B> and <B>radius_vert</B>: the
search radii in the maximum horizontal direction, minimum horizontal
direction, and vertical direction (see angles below).
<LI><B>sang1, sang2</B> and <B>sang3:</B> the angle parameters that describe
the orientation of the search ellipsoid. See the discussion on anisotropy
specification associated with Figure II.4.
<LI><B>ktype:</B> the kriging type (0 = simple kriging, 1 = ordinary
kriging, 2 = simple kriging with a locally varying mean, 3 = kriging with an
external drift, or 4 = collocated cokriging with one secondary variable)
used throughout the loop over all nodes. SK is required by theory; only in
cases where the number of original data found in the neighborhood is large
enough can OK be used without the risk of spreading data values beyond their
range of influence
<LI><B>rho:</B> correlation coefficient to use for collocated cokriging
(used only if <B>ktype</B> = 4).
<LI><B>secfl:</B> the file for the locally varying mean, the external drift
variable, or the secondary variable for collocated cokriging (the secondary
variable must be gridded at the same resolution as the model being
constructed by <TT>sgsim</TT>).
<LI><B>nst</B> and <B>c0:</B> the number of semivariogram structures and the
isotropic nugget constant.
<LI>For each of the <B>nst</B> nested structures one must define <B>it</B>,
the type of structure; <B>cc</B>, the <I>c</I> parameter;
<B>ang1,ang2,ang3</B>, the angles defining the geometric anisotropy;
<B>aa_hmax</B>, the maximum horizontal range; <B>aa_hmin</B>, the minimum
horizontal range; and <B>aa_vert</B>, the vertical range. </LI></UL>
<DT><IMG height=14 alt=o src="GSLIB Help SGSIM.files/ball.red.gif" width=14>
<STRONG>Application notes:</STRONG>
<UL>
<LI>This program requires standard normal data and writes standard normal
simulated values. Normal score transform and back transform are to be
performed outside of this program
<LI>Recall that the power model is not a legitimate model for a
multiGaussian phenomenon and it is not allowed in <TT>sgsim</TT>
<LI>The semivariogram model is that of the normal scores. The kriging
variance is directly interpreted as the variance of the conditional
distribution; consequently, the nugget constant <B>c0</B> and <B>c</B>
(sill) parameters should add to 1.0. </LI></UL></DT></DL><IMG height=8 alt=---
src="GSLIB Help SGSIM.files/line.blue.gif" width=652>
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