all functions - h

 
h_array

    name_array = h_array(f, ublk, name)  
 or pname_arrays = h_array(f, ublk, [name1,name2,...,nameN])  
    eq_nocopy, name_array1, *pname_arrays(1)  
    ...  
    eq_nocopy, name_arrayN, *pname_arrays(N)  


reads variable array NAME for user block UBLK from the hydra file F.    
If NAME=="matlist", you get the "Materials_matlist" array.  
Coordinates can be obtained using the names x, y or z.  
Ublk numbering starts at 0.  You can omit the UBLK argument and it  
will default to zero, which is useful for problems with only a single  
user block.  
Note that here zone centered arrays are given using the hydra convention  
so that i=imax, j=jmax, k=kmax are missing.  Thus in order to use the   
Yorick plc and plf functions correctly you should index the plotted  
variable i.e. for a 2D array.  
plf, den(1:-1,1:-1), y, x  
Interpreted function, defined at i/hydra.i   line 879  

SEE ALSO: hydra_xyz,   h_data,   h_mix,   h_show,   h_collect  
 
 
 

h_blocks

    gnblk = h_blocks(f, mdims, mlens)  


returns number of blocks GNBLK, block dimensions MDIMS, and  
block lengths MLENS for the hydra mesh in file F.  
MDIMS is 3-by-NBLK, MLENS is GNBLK elements.  
Interpreted function, defined at i/hydra.i   line 1191  

SEE ALSO: hydra_xyz,   h_iparm  
 
 
 

h_close

    h_close, f  


close a file F opened with h_openb.  
Interpreted function, defined at i/hydra.i   line 178  

SEE ALSO: h_openb  
 
 
 

h_collect

    vart = h_collect(f, ublk, name)  


returns an array of the variable NAME (a string) from user block  
UBLK of hydra file family F.  The return value has the leading  
dimensions of h_array(f,ublk,name), with a trailing dimension  
representing all the times in the family.  
Interpreted function, defined at i/hydra.i   line 962  

SEE ALSO: h_array,   h_show  
 
 
 

h_data

    name_array = h_data(f, name)  
 or pname_arrays = h_data(f, [name1,name2,...,nameN])  
    eq_nocopy, name_array1, *pname_arrays(1)  
    ...  
    eq_nocopy, name_arrayN, *pname_arrays(N)  


reads variable NAME from the hydra file F.  If F is a multiblock  
file, NAME_ARRAY will be 1-D; for single block problems it will  
be 3-D.  If NAME=="matlist", you get the "Materials_matlist"  
array.  Coordinates can be obtained using the names x, y or z.  
In the second form, NAME1, ..., NAMEN are retrieved simultaneously,  
which is useful when F is a large family of files.  
Note that zone centered arrays are adjusted to the hex convention  
that cells with i=1, j=1, k=1 are missing, rather than the hydra  
convention that i=imax, j=jmax, k=kmax are missing.  
Interpreted function, defined at i/hydra.i   line 626  

SEE ALSO: hydra_xyz,   h_mix,   h_array,   h_show,   hydra_aux_data  
 
 
 

h_fparm

    value = h_fparm(f, name)  
 or names = h_fparm(f)  


returns value of hydra parameter NAME from file F,  
or a list of all names in F if NAME is not supplied.  
If NAME is not a string, returns that parameter  
or parameters (NAME is index in the returned list of names),  
for example h_fparm(f,1:0) returns all parameters.  
Interpreted function, defined at i/hydra.i   line 1003  

SEE ALSO: hydra_xyz,   h_iparm,   h_parm  
 
 
 

h_gblk

    gblk = h_gblk(f)  


return global block information from the hydra file F (see h_openb).  
Each hblk in the mesh corresponds to a particular imin:imax,  
jmin:jmax, kmin:kmax in a particular gblk.  The return value is  
a 2D long array 7-by-numberof(h blocks):  
gblk(1,) =   user block number for this hblk  
gblk(2:3,) = gblk [imin,imax] of this hblk  
gblk(4:5,) = gblk [jmin,jmax] of this hblk  
gblk(6:7,) = gblk [kmin,kmax] of this hblk  
Interpreted function, defined at i/hydra.i   line 1102  

SEE ALSO: hydra_xyz,   h_data,   h_openb  
 
 
 

h_get_times

    times = h_get_times(f)  


return array of times in hydra history file family F.  
Interpreted function, defined at i/hydra.i   line 193  

SEE ALSO: h_data,   h_openb,   h_jt,   h_jr  
 
 
 

h_global

    value = h_global(f, name)  


returns value of hydra Global variable NAME from file F.  
Interpreted function, defined at i/hydra.i   line 1090  

SEE ALSO: hydra_xyz,   h_iparm  
 
 
 

h_iparm

    value = h_iparm(f, name)  
 or names = h_iparm(f)  


returns value of hydra parameter NAME from file F,  
or a list of all names in F if NAME is not supplied.  
If NAME is not a string, returns that parameter  
or parameters (NAME is index in the returned list of names),  
for example h_iparm(f,1:0) returns all parameters.  
Interpreted function, defined at i/hydra.i   line 986  

SEE ALSO: hydra_xyz,   h_fparm,   h_parm  
 
 
 

h_jr

    h_jr, f, irec  
 or nrecs = h_jr(f)  


jump to record IREC in hydra history file family F.  
In second form, return total number of records in family.  
Interpreted function, defined at i/hydra.i   line 224  

SEE ALSO: h_data,   h_openb,   h_get_times,   h_jt,   h_collect  
 
 
 

h_jt

    h_jt, f, time  


jump to time TIME in hydra history file family F.  
Interpreted function, defined at i/hydra.i   line 204  

SEE ALSO: h_data,   h_openb,   h_get_times,   h_jr,   h_collect  
 
 
 

h_mix

    mixdat = h_mix(f, matlist)  
    eq_nocopy, mixn, *mixdat(1)  
    eq_nocopy, mixcell, *mixdat(2)  
    eq_nocopy, mixnmat, *mixdat(3)  
    eq_nocopy, mixhist, *mixdat(4)  
 or mix_array = h_mix(f, mixdat, name)  
 or pmix_array = h_mix(f, matlist, [name1,...,nameN], mixdat)  
    eq_nocopy, mix_array1, *pmix_array(1)  
    ...  
    eq_nocopy, mix_arrayN, *pmix_array(N)  


In first form, returns MIXDAT and MATLIST for the hydra file F.  
MIXDAT consists of two arrays: MIXN is a list of the number of  
mixed cells for each block, and MIXCELL is an index array  
into any hex global cell array (as returned by h_data),  
MIXNMAT is the number of mix "zones" within each cell,  
and MIXHIST is the list required in order to use the  
histogram function on a mix array.  
In the second form, reads the mix data for the variable NAME  
in the hydra file F; the MIXDAT argument must have been returned  
by a previous call to h_mix using the first form.  
In the third form, MATLIST and MIXDAT are both returned along  
with the set of variables NAME1, ..., NAMEN, so that a number of  
variables can be retrieved in one call (useful when F is a large  
family of files).  
For example, to compute the temperature in each cell, using  
a mass weighted average in mixed zones, you would do this:  
  den = h_data(f,"den");  
  tmat = h_data(f,"tmat");  
  mixdat = h_mix(f, matlist);  
  local mixcell, mixhist;  
  eq_nocopy, mixcell, *mixdat(2);  
  eq_nocopy, mixhist, *mixdat(4);  
  denx = h_mix(f, mixdat, "den");  
  tmatx = h_mix(f, mixdat, "tmat");  
  vf = h_mix(f, mixdat, "vf");  
  tavg = tmat;  
  tavg(mixcell) = histogram(mixhist, tmatx*denx*vf)/den(mixcell);  
Interpreted function, defined at i/hydra.i   line 698  

SEE ALSO: hydra_xyz,   h_data,   h_array,   h_show  
 
 
 

h_openb

    f = h_openb(filename)  


open a hydra dump file, including 2D families of distributed  
history files.  
The return value is a list (see _lst function) containing the  
currently opened file and the non-PDB data required to navigate  
through each file and the entire family.  
With one=1 keyword, only one file of a history family is opened.  
Interpreted function, defined at i/hydra.i   line 42  

SEE ALSO: h_close,   hydra_xyz,   h_data,   h_jt,   h_jr,   h_get_times  
 
 
 

h_parm

    value = h_parm(f, name)  
 or names = h_parm(f)  


returns value of hydra parameter NAME from file F,  
or a list of all names in NAME is not supplied.  
Interpreted function, defined at i/hydra.i   line 1020  

SEE ALSO: hydra_xyz,   h_fparm,   h_iparm  
 
 
 

h_show

    h_show, f  
 or varnames = h_show(f)  


prints names of variables available for h_data, h_mix, h_array.  
Interpreted function, defined at i/hydra.i   line 251  

SEE ALSO: h_data,   h_openb  
 
 
 

h_ublk

    ublk = h_ublk(f)  
 or ublk = h_ublk(f, unew)  


return user block information from the hydra file F (see h_openb).  
Each ublk in the mesh has a particular size.  The return value is  
a 2D long array 7-by-numberof(u blocks):  
ublk(1,) =   user block number for this ublk  
ublk(2:3,) = ublk [imin,imax] of this ublk  
ublk(4:5,) = ublk [jmin,jmax] of this ublk  
ublk(6:7,) = ublk [kmin,kmax] of this ublk  
Normally, imin=jmin=kmin=1, and the only information in the return  
value is imax, jmax, kmax.  
In the second form, sets the ublk to UNEW, which is useful for  
resetting imin, jmin, and kmin for each block so that it describes  
a packing of the user blocks into an overall global block  
structure.  
Interpreted function, defined at i/hydra.i   line 1124  

SEE ALSO: hydra_xyz,   h_data,   h_openb  
 
 
 

hardbc

    hardbc  


  
     Interpreted function, defined at i/demo1.i   line 98  

 

has_records

    has_records(file)  


returns 1 if FILE has history records, 0 if it does not.  
Interpreted function, defined at i0/std.i   line 3296  

 

hcp

    hcp  
    hcpon  
    hcpoff  


The hcp command sends the picture displayed in the current graphics  
window to the hardcopy file.  (The name of the default hardcopy file  
can be specified using hcp_file; each individual graphics window may  
have its own hardcopy file as specified by the window command.)  
The hcpon command causes every fma (frame advance) command to do  
and implicit hcp, so that every frame is sent to the hardcopy file.  
The hcpoff command reverts to the default "demand only" mode.  
Builtin function, documented at i0/graph.i   line 318  

SEE ALSO: window,   fma,   plg,   pdf,   eps,   hcps  
 
 
 

hcp_file

    hcp_file, filename, dump=0/1, ps=0/1  


sets the default hardcopy file to FILENAME.  If FILENAME ends with  
".cgm", the file will be a binary CGM, otherwise it will be a  
Postscript file.  By default, the hardcopy file name will be  
"Aa00.ps", or "Ab00.ps" if that exists, or "Ac00.ps" if both  
exist, and so on.  The default hardcopy file gets hardcopy from all  
graphics windows which do not have their own specific hardcopy file  
(see the window command).  If the dump keyword is present and non-zero,  
the current palette will be dumped at the beginning of each frame  
of the default hardcopy file (default behavior).  With dump=0,  
all colors are converted to a gray scale, and the output files are  
smaller because no palette information is included.  
Use ps=0 to make "Aa00.cgm", "Ab00.cgm", etc by default instead of  
Postscript.  
The dump= and ps= settings persist until explicitly changed by a  
second call to hcp_file; the dump=1 setting becomes the default for  
the window command as well.  
Builtin function, documented at i0/graph.i   line 111  

SEE ALSO: window,   fma,   hcp,   plg  
 
 
 

hcp_finish

    filename= hcp_finish()  
 or filename= hcp_finish(n)  


closes the current hardcopy file and returns the filename.  
If N is specified, closes the hcp file associated with window N  
and returns its name; use hcp_finish(-1) to close the default  
hardcopy file.  
Builtin function, documented at i0/graph.i   line 132  

SEE ALSO: window,   fma,   hcp,   hcp_out,   plg  
 
 
 

hcp_out

    hcp_out  
 or hcp_out, n  


finishes the current hardcopy file and sends it to the printer.  
If N is specified, prints the hcp file associated with window N;  
use hcp_out,-1 to print the default hardcopy file.  
Unless the KEEP keyword is supplied and non-zero, the file will  
be deleted after it is processed by gist and sent to lpr.  
Interpreted function, defined at i0/graph.i   line 142  

SEE ALSO: window,   fma,   hcp,   hcp_finish,   plg  
 
 
 

hcpoff

    hcpoff  


Builtin function, documented at i0/graph.i   line 318  

SEE hcp  
 
 
 

hcpon

    hcpon  


Builtin function, documented at i0/graph.i   line 318  

SEE hcp  
 
 
 

hcps

    hcps, name  


writes the picture in the current graphics window to the  
PostScript file NAME+".ps" (i.e.- the suffix .ps is added to NAME).  
Legends are not written, but the palette is always dumped.  
Interpreted function, defined at i0/graph.i   line 163  

SEE ALSO: hcps,   window,   fma,   hcp,   hcp_finish,   plg  
 
 
 

help

    help, topic  
 or help  


Prints DOCUMENT comment from include file in which the variable  
TOPIC was defined, followed by the line number and filename.  
By opening the file with a text editor, you may be able to find  
out more, especially if no DOCUMENT comment was found.  
Examples:  
  help, set_path  
prints the documentation for the set_path function.  
  help  
prints the DOCUMENT comment you are reading.  
This copy of Yorick was launched from the directory:  
**** Y_LAUNCH (computed at runtime) ****  
Yorick's "site directory" at this site is:  
**** Y_SITE (computed at runtime) ****  
You can find out a great deal more about Yorick by browsing  
through these directories.  Begin with the site directory,  
and pay careful attention to the subdirectories doc/ (which  
contains documentation relating to Yorick), and i/ and  
contrib/ (which contain many examples of Yorick programs).  
Look for files called README (or something similar) in any  
of these directories -- they are intended to assist browsers.  
The site directory itself contains std.i and graph.i, which  
are worth reading.  
Type:  
  help, dbexit  
for help on debug mode.  If your prompt is "dbug>" instead of  
">", dbexit will return you to normal mode.  
Type:  
  quit  
to quit Yorick.  
Builtin function, documented at i0/std.i   line 33  

SEE ALSO: quit,   info,   print,   copyright,   warranty,   legal  
 
 
 

help_worker

    help_worker  


  
     Interpreted function, defined at i0/std.i   line 99  

 

hex24b_track

    hex24b_track  


Builtin function, documented at i0/hex.i   line 40  

SEE hex5_track  
 
 
 

hex24f_track

    hex24f_track  


Builtin function, documented at i0/hex.i   line 40  

SEE hex5_track  
 
 
 

hex5_track

    c= hex5_track(mesh, rays, s)  
    c= hex24f_track(mesh, rays, s)  
    c= hex24b_track(mesh, rays, s)  


track 3 x Nrays x 2 RAYS through the 3D MESH.  RAYS(,,1) are  
points on the rays, while RAYS(,,2) are normalized ray directions.  
The c return value and the S parameter are a long and double  
array respectively, with number of elements equal to the total  
number of intersections of all the RAYS with faces of the MESH,  
plus one for any RAY which misses MESH entirely.  The values of  
c are:  
  [#hits,cell1,cell2,cell3,..., #hits,cell1,cell2,cell3,..., ...]  
where each #hits is followed by the list of cell indices (assuming  
i=1, j=1, and k=1 are present but meaningless in cell arrays --  
that is, assuming zone centered arrays have the same dimensions  
as XYZ rather than one less in each direction).  Rays which miss  
the mesh entirely have #hits=1, all others have #hits>=2 since they  
must exit.  #hits<0 means a ray reentered the mesh for abs(#hits)  
more face crossings, but this currently cannot happen.  The values  
of S correspond to c:  
  [s0,s1,s2,s3,..., s0,s1,s2,s3,..., ...]  
which are the distances along the ray measured from RAYS(,,1) in  
the direction of RAYS(,,2) where the ray pierces a cell face.  For  
rays which miss the mesh, the value of s0 is a diagnostic telling  
why they missed (see compiled code).  
Function hex5_track uses the 5-tet decomposition for hexes,  
which is not unique when the quad faces are non-planar.  You may  
be able to get an idea of this effect by setting hex_triang the  
opposite way and redoing the trace.  
Functions hex24f_track and hex24b_track use the face and body  
centered 24-tet decompositions for hexes.  These are unique;  
however, hex_triang may in rare cases change the trace slightly,  
since the entry search algorithm still involves triangulating  
the surface quads.  
Builtin function, documented at i0/hex.i   line 40  

SEE ALSO: hydra_mesh,   hex_triang,   reg_track,   track_reduce,   c_adjust,   pic3_rays,  
conv3_rays  

 
 
 

hex_mesh

    mesh= hex_mesh(xyz, bound, nbnds, &mbnds, nblk, &blks, start)  


create a 3D mesh object from the multiblock mesh parameters  
XYZ   is NBLK 3 x Ni x Nj x Nk coordinate arrays packed together  
BOUND is NBLK 3 x Ni x Nj x Nk face boundary markers packed  
NBNDS is length of MBNDS  
MBNDS is HX_blkbnd describing each internal block boundary face  
NBLK  is number of blocks  
BLKS  is NBLK HX_block objects describing the block structure  
START is 0-origin 6*cell+face index of first boundary face/cell  
       or -1-cell to trace from centroid of that cell to point  
       p on ray to begin tracking  
Builtin function, documented at i0/hex.i   line 12  

SEE ALSO: hex5_track,   hydra_mesh,   hex_startflag  
 
 
 

hex_mesh2

    mesh= hex_mesh2(xyz, bounds)  


old interface for hex_mesh  
create a 3D mesh object from the 3 x Ni x Nj x Nk coordinate  
array XYZ and the list of 6 BOUNDS:  
  BOUNDS(1), BOUNDS(2)  for the i=1,Ni boundaries  
  BOUNDS(3), BOUNDS(4)  for the j=1,Nj boundaries  
  BOUNDS(5), BOUNDS(6)  for the k=1,Nk boundaries  
The BOUNDS values are:  
  1   if this is a problem boundary  
  2   if this is a reflecting boundary  
  3   if this is a periodic boundary  
Interpreted function, defined at i0/hex.i   line 692  

SEE ALSO: hydra_mesh  
 
 
 

hex_query

    start= hex_query(mesh, xyz, bound, mbnds, blks)  


query a mesh created by hex_mesh, returning the arrays  
passed to that function (these are not copies -- be careful  
not to clobber them)  
function return value is the start index  
Builtin function, documented at i0/hex.i   line 29  

SEE ALSO: hex5_track,   hydra_mesh  
 
 
 

hex_startflag

    old_flag= hex_startflag(new_flag)  


possibly set flag to NEW_FLAG, always return OLD_FLAG, where  
flag value is 0 (default) to begin search for new entry point  
at previous entry point, 1 to begin search for new entry point  
from mesh start face for every ray.  Any other value of NEW_FLAG  
returns OLD_FLAG without changing it.  
Builtin function, documented at i0/hex.i   line 596  

SEE ALSO: hex_mesh  
 
 
 

hex_triang

    old_flag= hex_triang(new_flag)  


possibly set flag to NEW_FLAG, always return OLD_FLAG, where  
flag value is 0 for default mesh triangulation, 1 for opposite  
triangulation, and 2 on input to signal not to change the  
current value.  The triangulation value can affect the result  
of hex5_track if the quad faces of the mesh are not planar.  
Builtin function, documented at i0/hex.i   line 581  

SEE ALSO: hex5_track  
 
 
 

histeq_scale

    histeq_scale(z, top=top_value, cmin=cmin, cmax=cmax)  


returns a byte-scaled version of the array Z having the property  
that each byte occurs with equal frequency (Z is histogram  
equalized).  The result bytes range from 0 to TOP_VALUE, which  
defaults to one less than the size of the current palette (or  
255 if no pli, plf, or palette command has yet been issued).  
If non-nil CMIN and/or CMAX is supplied, values of Z beyond these  
cutoffs are not included in the frequency counts.  
Interpreted function, defined at i0/graph.i   line 1466  

SEE ALSO: bytscl,   plf,   pli  
 
 
 

histinv

    list = histinv(hist)  


returns a list whose histogram is HIST, hist = histogram(list),  
that is, hist(1) 1's followed by hist(2) 2's, followed by hist(3)  
3's, and so on.  The total number of elements in the returned  
list is sum(hist).  All values in HIST must be non-negative;  
if sum(hist)==0, histinv returns [].  The input HIST array may  
have any number of dimensions; the result will always be either  
nil or a 1D array.  
Interpreted function, defined at i0/std.i   line 1160  

SEE ALSO: histogram  
 
 
 

histogram

    histogram(list)  
 or histogram(list, weight)  


  returns an array hist which counts the number of occurrences of each  
  element of the input index LIST, which must consist of positive  
  integers (1-origin index values into the result array):  
       histogram(list)(i) = number of occurrences of i in LIST  
  A second argument WEIGHT must have the same shape as LIST; the result  
  will be the sum of WEIGHT:  
       histogram(list)(i) = sum of all WEIGHT(j) where LIST(j)==i  
  The result of the single argument call will be of type long; the  
  result of the two argument call will be of type double (WEIGHT is  
  promoted to that type).  The input argument(s) may have any number  
  of dimensions; the result is always 1-D.  
KEYWORD: top=max_list_value  
  By default, the length of the result is max(LIST).  You may  
  specify that the result have a larger length by means of the TOP  
  keyword.  (Elements beyond max(LIST) will be 0, of course.)  
  Builtin function, documented at i0/std.i   line 1135  

SEE ALSO: digitize,   sort,   histinv  
 
 
 

hydra_adj

    hydra_adj  


  
     Builtin function, documented at i0/hex.i   line 630  

 

hydra_blks

    hydra_blks  


  
     Builtin function, documented at i0/hex.i   line 611  

 

hydra_bnd

    hydra_bnd  


  
     Builtin function, documented at i0/hex.i   line 616  

 

hydra_mesh

    mesh= hydra_mesh(f)  
 or mesh= hydra_mesh(f, ublk, i0, j0, k0, face)  
 or mesh= hydra_mesh(f, ublk, i0, j0, k0)  


read a 3D mesh object from the hydra PDB/Silo file F.  
Note that the boundary arrays are adjusted to the hex convention  
that cells with i=1, j=1, k=1 are missing, rather than the hydra  
convention that i=imax, j=jmax, k=kmax are missing.  
In the first form, the ray entry search will start on the  
first open boundary face in the mesh.  If the actual problem  
boundary is not convex, you need to identify a surface of  
constant i, j, or k in the problem which is convex, and which  
all the rays you intend to trace intersect.  
UBLK is the user block number (starting from 0),  
I0, J0, K0 are the (1-origin) logical coordinates of a  
  hydra *cell*.  Note that unlike hex cells, the hydra  
  cell bounded by nodes (1,1,1) and (2,2,2) is numbered (1,1,1).  
  (Hex numbers it (2,2,2).)  
FACE is the face number on cell (I0,J0,K0) which you want a  
  ray to enter.  0 means the -I face, 1 the +I face, 2 the -J  
  face, 3 the +J face, 4 the -K face, and 5 the +K face.  
  As you step from this cell to its neighbors, then to their  
  neighbors, and so on, this face must trace out a convex  
  surface for the ray entry search.  Rays not intersecting  
  this surface will not enter the problem; the ray trace  
  will begin at this surface, not at -infinity.  
If FACE==-1 or is omitted (as in the third form), then the  
given points on the rays are assumed to lie inside the mesh,  
and a pseudo ray from the centroid of cell (I0, J0, K0) will be  
tracked to the given point on each ray; the ray will be launched  
into the cell containing that point.  
Interpreted function, defined at i0/hex.i   line 638  

SEE ALSO: hex_query,   hex5_track,   h_data,   h_openb  
 
 
 

hydra_mrk

    hydra_mrk  


  
     Builtin function, documented at i0/hex.i   line 624  

 

hydra_start

    hydra_start, mesh, start  


change the starting cell of the hydra MESH (returned by hydra_mesh)  
to START.  If called as a function, returns old start value.  
Interpreted function, defined at i0/hex.i   line 784  

SEE ALSO: hydra_mesh,   h_data  
 
 
 

hydra_xyz

    mesh = hydra_xyz(f)  
 or mesh = hydra_xyz(f, ublk, i0, j0, k0, face)  
 or mesh = hydra_xyz(f, ublk, i0, j0, k0)  


read a 3D mesh object from the hydra PDB/Silo file F.  
The returned mesh is _lst(xyz, bound, mbnds, blks, start).  
Note that the boundary arrays are adjusted to the hex convention  
that cells with i=1, j=1, k=1 are missing, rather than the hydra  
convention that i=imax, j=jmax, k=kmax are missing.  
In the first form, the ray entry search will start on the  
first open boundary face in the mesh.  If the actual problem  
boundary is not convex, you need to identify a surface of  
constant i, j, or k in the problem which is convex, and which  
all the rays you intend to trace intersect.  
UBLK is the user block number (starting from 0),  
I0, J0, K0 are the (1-origin) logical coordinates of a  
  hydra *cell*.  Note that unlike hex cells, the hydra  
  cell bounded by nodes (1,1,1) and (2,2,2) is numbered (1,1,1).  
  (Hex numbers it (2,2,2).)  
FACE is the face number on cell (I0,J0,K0) which you want a  
  ray to enter.  0 means the -I face, 1 the +I face, 2 the -J  
  face, 3 the +J face, 4 the -K face, and 5 the +K face.  
  As you step from this cell to its neighbors, then to their  
  neighbors, and so on, this face must trace out a convex  
  surface for the ray entry search.  Rays not intersecting  
  this surface will not enter the problem; the ray trace  
  will begin at this surface, not at -infinity.  
If FACE==-1 or is omitted (as in the third form), then the  
given points on the rays are assumed to lie inside the mesh,  
and a pseudo ray from the centroid of cell (I0, J0, K0) will be  
tracked to the given point on each ray; the ray will be launched  
into the cell containing that point.  
You can set a hydra_bnd_hook function before calling hydra_xyz  
if the boundary conditions for hex need to be different than  
for hydra.  
Interpreted function, defined at i/hydra.i   line 285  

SEE ALSO: hydra_bnd_hook,   h_data,   h_openb,   hydra_aux_data,   hydra_mix_data