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README
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#########################################
# hemeXtract documentation and examples #
#########################################
INSTALLING:
----------
Just run make
...hopefully.
GENERAL HELP:
------------
For help on all hemeXtract options, you can use the --help (or -h) option:
./hemeXtract --help
EXTRACTING FROM A SINGLE FILE:
-----------------------------
To simply extract the data in a single file, use the -X option.
For example, the following command will dump every grid site in the file for every snapshot (a lot of data!):
./hemeXtract -X out.xtr
However, if you instead wish to calculate some statistics (average, max and min velocity, std deviation etc.), use the --stats (or -s) option:
./hemeXtract -X out.xtr --stats
This still analyses every snapshot. If you only want to consider snapshots from a specific time window, you can use the following:
./hemeXtract -X out.xtr --stats --time1=1.1 --time2=4.7 --steplengthA=1e-4
This will only act on snapshots between 1.1s and 4.7s (inclusive). Note that the step length of the original simulation has to be specified, since
HemeLB does not output that to the xtr files. By default, if not specified, --time1 will be 0, --time2 will be INFINITY, and --steplengthA will be 1.
If you want to enforce a maximum number of snapshots output, you can use the --numsnapshots option. For example:
./hemeXtract -X out.xtr --stats --time1=2.0 --steplengthA=1e-4 --numsnapshots=5
will calculate the stats for (up to) 5 snapshots, starting at time 2.0s.
Finally, all of the above dump straight to stdout. If you wish for hemeXtract to write to an output file instead, use the --output option.
e.g.
./hemeXtract -X out.xtr --stats --output=stats_output.txt
COMPARING TWO FILES:
-------------------
hemeXtract can also compare two HemeLB extraction files in a variety of ways. To do this, use the -C option. For example:
./hemeXtract -C planeA.xtr planeB.xtr
This will calculate the difference (L2 norm of the difference) between the velocity at each site in A and its corresponding
site in B. If A and B have different resolutions, hemeXtract will calculate the mapping between the lattices, and use trilinear
interpolation to find the corresponding value in B for each A. This therefore gives the "error" or "difference" at each site.
If we instead wish to calculate comparison stats for the whole lattice, we can once again use --stats:
./hemeXtract -C planeA.xtr planeB.xtr --stats
This will print out the crosscorrelation of velocity, shearstress and pressure between the two lattices, as well as the max. and min. velocity in each.
As for single file extraction, if we want to look only at snapshots in a given time range, we can use --time1, --time2, --steplengthA and --steplengthB
e.g.
./hemeXtract -C planeA.xtr planeB.xtr --stats --time1=2.0 --time2=3.5 --steplengthA=1e-4 --steplengthB=1e-5
will calculate the correlations etc. for planeA.xtr and planeB.xtr between the (real) times of 2.0s and 3.5s. As before, the
step length used in the simulation of planeA (--steplengthA) and that used in the simulation of planeB (--steplengthB).
--output and --numsnapshots can also be used, as for the single file extraction case.
UNDERSTANDING THE OUTPUT:
------------------------
Different modes and options change what hemeXtract outputs. If you wish to know what each column of output refers to, look at the beginning of the output: there
will be a line giving the column headings.