Description

This document describes the functions provided by the Varmm library (Variable, Math and Macro) and how they can be used in S-Lang code. Additional useful information can be found using "ahelp slang", "ahelp variables", "ahelp math", and "ahelp tips".

The Varmm library is automatically loaded into Sherpa and ChIPS and can be loaded into any S-Lang code by saying

require("varmm");

Note that if you have already loaded the Sherpa or ChIPS S-Lang modules into your S-Lang code then you do not need to load in Varmm as well.

Varmm provides a number of functions for reading data from files (both ASCII and FITS formats), and assigning them to variables. In addition to Varmm, there are many I/O functions within S-Lang itself which can also be used; these functions resemble their C counterparts, such as fopen() and fread(). Varmm also contains a number of utility functions; use "ahelp <function>" to get a detailed description of a particular function or "ahelp -c varmm" to get a list of all these functions.

Customizing the S-Lang run-time environment

The Varmm library allows customization of your S-Lang run-time environment through the use of a resource file ($HOME/.varmmrc, discussed below) and the varmmrl module, described in "ahelp varmmrl".

If the file .varmmrc exists in your home directory, then the Varmm library will assume it contains a series of valid S-Lang commands and read it using evalfile(). This is a simple but powerful extension that permits essentially arbitrary S-Lang scripts/functions to be shared amongst any Varmm-enabled application (currently ChIPS and Sherpa). For example, if the following were stored in your $HOME/.varmmrc

  define compute_average (x, y)
  {
      variable s = x + y;
      return s / 2.0;
  }

then the function compute_average() would be available to each instance of Sherpa and ChIPS. The use of this feature should probably be restricted to often-used code, since it is read in and parsed every time a Varmm-aware CIAO application is started.

The Varmm state object

Another way that Varmm can be customized is through the Varmm state object. The varmm object contains a number of fields that can be used to change the default behaviour of Varmm functions (for instance by setting them in your $HOME/.varmmrc file).

The Varmm state object

Currently only the readheader and caseinsen parameters are used, as discussed in "ahelp readfile". To see the current settings, you can use print and manipulate individual fields:

  chips> print(varmm)
  readheader      =  1
  rawkeys         =  1
  verbosity       =  1
  caseinsen       =  0
  chips> varmm.caseinsen = 1

and the set_state_defaults() and set_state() commands can be used to make wholesale changes to the object.

Using Varmm in your own S-Lang code

The following is not necessary if you are executing S-Lang code from ChIPS or Sherpa, since they already load the Varmm library, but is required if you are using a different S-Lang interpreter, such as slsh. The Varmm library can be made available by using the S-Lang "require()" command in your script:

  require("varmm");

You do not need to do this if the script also uses ChIPS or Sherpa S-Lang functions, since Varmm is automatically loaded when you do

require("chips");

or

require("sherpa");