Some of the parameters to Yafit tasks allow you to enter an
algebraic expression in terms of named variables or column names.
For instance the x and y parameters in the
tableobs and
copymodel have values
which are expresions. This section explains the expression language
that is used.
Form most purposes, the language is pretty intutive. The normal
algebraic operators
(+, -, * and /)
are available, numbers are written in the usual way, and variable
names such as those representing table columns
must start with a letter and continue with a sequence of letters,
numbers and underscores.
As well as these, there are a number of pre-defined functions which
can be used. As well as standard ones such as exp(),
cos(), max(), sqrt() and so on,
there are some useful astronomically specific ones, including
luminosityDistance(z,H0,omegaM,omegaLambda)
mToMpc(distMetres)
abToJansky(magAB)
janskyToAb(fluxJansky)
funcs task.
The expression language is powerful and extensible, however, most users of Yafit will not need to use many of its features, so it is not discussed in detail here. For a full description see the manuals for STILTS or TOPCAT, which use the same technology.