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bodytrans - test and optionally save body to scalar mapping
expr=expression [parameter=value] ...
bodytrans is a testbed for
saving/debugging a user-specified mapping from a body(3NEMO)
to a real or
integer value. These mappings are given by an arbitrary C expression involving
any of the variables m, x, y, z, vx, vy, vz, phi, ax, ay, az, aux, key,
t, and i, using various math library functions, e.g. cbrt(), sqrt(), qbe(),
sqr(), sin(), cos(), asin(), acos(), tan(), atan(), atan2(), exp(), dex(),
log(), log10(), pow(), fabs(), floor(), ceil(), and rint(). (assuming
3 dimensional body’s, see ENVIRONMENT below).
Given such an expression, bodytrans
invokes the C compiler, which is general but can be rather slow. To speed
things up, an expression is first treated as a name and checked against
a collection of precompiled expressions stored as ".o" (see a.out(5)
If the expression is a real/int expression, it will search for an object
file btr_expr.o, bti_expr.o resp. If a match is found, the precompiled object
is used instead. If bodytrans has been compiled with auto-saving object
files a next search will be performed on the $NEMOOBJ/bodytrans/BTNAMES
database. This contains a list of expressions and names of their object
files, these object files were previously generated by any program which
used the bodytrans(3NEMO)
A number of precompiled transformations
already exist, e.g.: x, y, z, vx, vy, vz, r, v, vr, vt, jtot, phi, etot,
t, and i. A complete list may be deduced by looking in $NEMOOBJ/bodytrans/,
which is the default repository. It is possible to customize your own transformations
and collections; see $NEMO/src/nbody/core/bodysub/ for model routines.
If bodytrans has been compiled with auto-saving (the default), the object
file will be saved in the standard repository directory $NEMOOBJ/bodytrans,
and the corresponding database file-list BTNAMES will be updated. When using
the same expression expr at a later time not only can the user then refer
to the expression by it’s original expression, but also by its pseudo-name
file (see keyword file and examples below).
For an alternative approach
to use dynamic analysis routines, see mkbodyfunc(1falcON)
The following parameters are recognized.
The following command
C-language expression specifying the transformation to test. If keyword file
is present (see below) a mapping file of the name btX_file is tried before
the expression is turned into a mapping file. Default: x.
- Type of value returned; currently either real or int. Default: real.
- Mass of body used to test mapping. Default: 0.125.
of body, specified by a comma-separated list of components. Default: 0.5,-0.5,1.0.
- Velocity of body. Default: 0.1,0.2,-0.3.
- Gravitational potential at position of body. Default: -1.2.
- Acceleration of body. Default: -0.5,0.7,0.1.
- Real auxiliary
value associated with body. Default: 3.141592.
- Integer key
value associated with body. Default: 3.
- Time value available
to expression. Default: 2.5.
- Body index available to expression.
- Tail of the filename under which the expr transformation
is to be saved for later recovery. Note that the first four characters of
the filename are already fixed and will be btX_, where X is either r or
i, depending on the type (see above) of the expression. The full filename
will hence be btX_file. [default: not used].
- File containing
a database of expression and filenames under which they are to be saved.
When used, the program (re) creates all bodytrans(5)
files and exits. [default:
- Show the currently saved bodytrans functions (from the
BTNAMES files). [Default: f].
% bodytrans expr=x+y+z alias=sum
saves the mapping in an object file btr_sum.o, and can be later used as
% snapprint snap-file x+y+z
or using this alias
% snapprint snap-file sum
It is not necessary to provide a pseudonym using the keyword alias, although
recommended if bodytrans is used. As an example, the command
% bodytrans expr=x+y+z
could save the mapping in an object file btr__24, and can later be referred
% snapprint snap-file x+y+z
or the more cryptic
% snapprint snap-file _24
The relationship between _24 and x+y+z is saved in the file BTNAMES and
resolved at run-time.
There is a shell script BTclean that selectively
cleans up object files listed in the BTNAMES file. A new ’BTNAMES’ file is
generated. You can run it interactively (have to be NEMO user though) and
answer some simple questions.
By default, body to scalar transformations
are applied to bodies which have vectors of lenght 3 (see also vectmath(3NEMO)
By adding -DTWODIM to the environment variable CFLAGS, newly created bodytrans
variables are compiled with 2D bodies. Obviously it is very dangerous to
mix 2D and 3D bodies, but the possibility exists.
Joshua E. Barnes, Peter Teuben
~/src/nbody/core/bodysub/* default standard bodytrans(5) files
xx-xxx-87 V1.0 Created JEB
8-jul-89 V1.1 saving bodytrans mappings into user files PJT
19-nov-89 V1.2 BTNAMES database used for saving PJT
10-dec-91 some more doc PJT
12-aug-92 documented CFLAGS usage PJT
2-aug-06 V3.3 add show= PJT
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