Parameters, parameter files, and history files

If you find yourself despairing at having to remember and type huge lists of parameters like

transp=y poly=y yreverse=y  pclip=100

again and again, you will be happy to know there is a shortcut. Try putting the list of parameters above into a text file called ``plotpar''. Put the windowing parameters

n2=10 n1=200 f1=200

into another file called ``windowpar''. Then you could do

Window < Txx.H par=windowpar | Wiggle par=plotpar | Tube

and it would be just like you had typed the full set of parameters at the ``par=plotpar'' and ``par=windowpar''. Files like ``plotpar'' and ``windowpar'' are called parameter files, and they can be nested simply by putting par= commands into the parameter files just like on the command line. An additional advantage of parameter files is that they can be as long as you want, so you don't have to cram everything onto one single line. (You can also put comments into a parameter file; anything after a ``#'' on a line in a parameter file is ignored, just like for csh scripts.)

What happens if the same parameter is set multiple times? The last occurrence is the only one that matters. You must pay special attention to how the parameters are written, though: a parameter can be ``unset'' by leaving the space after the ``='' blank. An = with a space before it is ignored completely.

In summary:
n1=1 sets n1 equal to 1;
n1= 1 would unset any previous setting of n1, letting it default.
n1 = 1 is a comment. It has NO EFFECT AT ALL on n1.

Now reread the previous paragraph again until you are sure you won't make the mistake of writing n2 = 10 and wondering why it didn't work.

You may have already realized that a history file is just a special kind of parameter file. Before checking for parameters on the command line, SEPlib first looks for any relevant parameters in the input history file. That's how ``Wiggle'' knew the dimensions of the data in Txx.H without having to be told. Of course, we can override the information in the input history file by setting another value on the command line. For example, if we do

Wiggle < Txx.H par=plotpar n1=5000 | Tube

Wiggle will happily attempt to read past the end of the floating-point data set, resulting in an error message

sreed: Illegal seek
Wiggle: xdr error reading from ``in''

For another example of overriding a parameter set by the history file, how about changing the title of our plot from the boring ``Txx'' set in the history file Txx.H?

Wiggle < Txx.H par=plotpar title="\s200 \F11 Slava \c2 Trudu" | Tube

This changes it to a good old-fashioned Russian title, ``Glory to Labor''! It is also possible to put superscripts, subscripts, etc, into labels and titles; do ``man vplottext'' for examples.

Even a single program like Wiggle has more options than we can hope to enumerate here. To see what other options are possible, look at the self-documentation and try them out. By all means don't neglect to check whether the program you are interested in might happen to have a manual page as well.