\section{Introduction}

\subsection{Philosophy}

\greg\ is a graphic utility package whose goal is to help people prepare
plots of their data or of the results of theoretical computations.  Major
goals were device independence as much as possible {\tt AND} efficient
interactive use. It was kept in mind that drawings are usually prepared
interactively and then the final result is sent to a good quality printer
or saved for later use. Quick look on data is also often wanted.  Hence,
the design goals were both a simple, fast utility for simple things and a
powerful, flexible system producing high quality plots.  In addition, it
was soon realised that a stand-alone utility was unadapted for complex,
repetitive integrated plots as often required in theoretical modelling.
Accordingly, the library version became part of the design goals.

With the advent of the X-Window system, GREG has been totally rewritten to
take advantage of the multi-window and color facilities of X-Window.  This
new version also handles bitmap display of images, contour filling,
etc\ldots, with hardcopy facilities on PostScript devices.

\subsection{Getting started}
 
Beginners should of course read Section 2, the beginner's guide.  While
doing this, you need only retain the topics with which you are concerned at
first view. If anything seems to be lacking, then read the other topics.
 
After a few trials (say a few days of normal usage or a few drawings), most
users will efficiently benefit from reading carefully Section 3. With some
more practice, they will soon reach normal proficiency in \greg\ standard
usage and be able to tackle the most funny things.

Section 4, the ``advanced'' user's guide, is important for those who want
to get the best of \greg\, with colours, images, etc... It is also
important for the application programmer who may use these features to
provide a top layer for integrated applications.

Section 5,6,7 contains descriptions of all \greg\ commands on a command by
command basis. This is a copy of the internal help.  Please keep in mind
that because of \greg\ evolution it may not be completely up to date.
 
At this stage, model builders (as opposed to observers) will most likely
want to go further by using the {\tt GREGLIB} and thus reading Section 8.
This may be done sooner, but it is not recommended to use the {\tt GREGLIB}
before the basic concepts of \greg\ have been mastered.

The documentation on the \sic\ monitor is now provided separately in the
manual \sic\ documentation, and at least the first chapter of this manual
should be read by the beginners.  The monitor offers many flexible
capabilities such as procedures, symbols, vector mathematics, and so on.
 
The other sections concern only programmers of special purpose tasks, or
system builders, and their lecture will be almost necessarily complemented
by reading the \sic\ manual also. Note however that if you have some
specific graphic problem, it is most likely solved somewhere in the \greg\ 
package, so that the answer may well be under these sections.
 
Know what you want ?  Then go ahead, and good luck.

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