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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
<html>
<head>
<title>AMR Grid Data Structure</title>
</head>
<body>
<body bgcolor="#F0F0F0">
<font face="arial,helvetica"><h1>AMR Grid Datastructure</h1></font>
Common to all of the AMR readers is an <b>AmrGrid</b>
informational datastructure. This datastructure is <i>not</i>
necessary for the <a href="AMRwriter.html">AMRwriter</a>.
This structure stores all of the
AMR parameters related to the grid that enable you to determine
where it should fit into the AMR hierarchy, the type of data
that it stores and the rank, dimensions, and physical size of
the grid. It also has a pointer which can be used optionally
to store the grid data.<p>
The structure has both a C and a C++ representation. The only
difference between the two is that the C structure represents
the datatype as an integer and the C++ version represents the
datatype as an enum. Since the C++ struct is inherited
directly from the C version, the two interoperate
seamlessly.<p>
<font face="arial,helvetica" color="#555588">
<h2>Datastructure Specification</h2>
</font>
<table border=1><tr>
<td>
<font face="arial,helvetica" color="#885555"><b>C Datastructure</b></font>
</td>
<td>
<font face="arial,helvetica" color="#885555"><b>C++ Datastructure</b></font>
</td>
</tr>
<tr><td>
<pre>
typedef struct AmrGrid {
int level;
int maxlevel;
int maxtime;
int timestep;
int persistence;
int rank;
int dims[3];
double delta[3];
double origin[3];
int timerefinement;
int nbytes;
int dataveclen;
int datatype;
void *data;
} AmrGrid;
</pre>
</td><td>
<pre>
struct AmrGrid {
// Members inherited from C AmrGrid
int level;
int maxlevel;
int maxtime;
int timestep;
int persistence;
int rank;
int dims[3];
double delta[3];
double origin[3];
int timerefinement;
int nbytes;
int dataveclen;
void *data;
// Members specific to C++ AmrGrid
IObase::DataType datatype;
};
</pre></td></tr></table>
<font face="arial,helvetica" color="#555588">
<h2>Datastructure Member Descriptions</h2>
</font>
<DL>
<DT><i>int</i> <b>level</b>
<DD>The level in the AMR hierarchy. Level 0 is the Top (least refined)
level.
<DT><i>int</i> <b>maxlevel</b>
<DD>The maximum number of levels in the AMR hierarchy for all
timesteps stored in this file. Levels are numbered from 0
to maxlevel-1.
<DT><i>int</i> <b>maxtime</b>
<DD>Maximum timestep in the datafile. This parameter is optional
<i>(and generally unused)</i> and will be removed from
future releases.
<DT><i>int</i> <b>timestep</b>
<DD>This is the current integer timestep with respect to the finest
granularity timestep that can occur in the file. It is not
necessarily uniform in time. It simply delineates the order
in which things change in the file. It is a fundamental
parameter written by the <a href="AMRwriter.html">AMRwriter</a>.
<DT><i>int</i> <b>persistence</b>
<DD>This is the number of timesteps that the grid remains active from
the timestep that it is created. Like the <b>timestep</b>
parameter, it can also be non-uniform. It is an optional
parameter that is often automatically computed by the
AMRreader class from available data.
<DT><i>int</i> <b>rank</b>
<DD>The number of dimensions for the grid. Currently you cannot mix
grids of different dimensions together (ie. a 2D grid cannot
be embedded in a 3D grid), so if one grid is rank=3, then
all of the grids in the file must have the same rank.
<DT><i>int</i> <b>dims[3]</b>
<DD>The dimensions of the grid (only the first <i>rank</i> values of
this array will be filled).
<DT><i>double</i> <b>delta[3]</b>
<DD>The physical spacing between gridpoints. This is actually
redundant information since the same information can be
inferred/computed from the <b>origin</b> and integer
refinement information. It is there for convenience though
even though it is not as precise as the integer specification.
<DT><i>double</i> <b>origin[3]</b>
<DD>The physical origin (minimum extent in 3-space) of the grid.
<DT><i>int</i> <b>timerefinement</b>
<DD>The rate at which the grid steps at this level with respect to the
topgrid. This is an optional parameter and will likely be
dropped from future implementations of this system.
<DT><i>int</i> <b>nbytes</b>
<DD>Number of bytes of storage required for the grid data if it were loaded
into memory.. This is useful for memory allocation/management.
<DT><i>int</i> <b>dataveclen</b>
<DD>The number of elements-per-point in the data. For instance a
3D vector velocity field would have a dataveclen=3 for the i,j,k
direction of the vector components. dataveclen=1 for all
scalar values like density and temperature.
Currently this is not
used, but will be in future implementations of the readers.
<DT><i>int/IObase::DataType</i> <b>datatype</b>
<DD>The type of the data as it is stored on disk. This is represented
as an <i>integer</i> for C and as an <i>enum</i> of type
<i>IObase::DataType</i> for C++. The definitions for the
<a href="DataTypes.html">datatypes are defined
by the FlexIO libraries</a>.
Integer datatypes are implemented in <a href="src/IO.h">IO.h</a>
and the C++ <i>IObase::DataType</i> is implemented in
<a href="src/IO.hh">IO.hh</a>.
<DT><i>void *</i><b>data</b>
<DD>Pointer to memory array storing the data. This is NULL
if the data has not been loaded into memory. So you can use
this datastructure just to aquire information about the
grids and then load the data only when it is needed.
</DL>
<hr>
<address><a href="mailto:jshalf@ncsa.uiuc.edu"></a></address>
<!-- Created: Thu Jan 28 12:40:39 CST 1999 -->
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Last modified: Thu Jan 28 17:14:34 CST 1999
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