Made class possymbol for positive symbols and documented it.

[ginac.git] / doc / tutorial / ginac.texi

diff --git a/doc/tutorial/ginac.texi b/doc/tutorial/ginac.texi
index 26f004ed73b2cf39efe9124f941741a1e14b4750..bdea81b80a842aa0c6c71a5b193dbcf8e8754f60 100644 (file)
--- a/doc/tutorial/ginac.texi
+++ b/doc/tutorial/ginac.texi
@@ -1155,11 +1155,17 @@ in the complex domain.  As a consequence, operations like complex conjugation,
 for example (@pxref{Complex expressions}), do @emph{not} evaluate if applied
 to such symbols. Likewise @code{log(exp(x))} does not evaluate to @code{x},
 because of the unknown imaginary part of @code{x}.
-On the other hand, if you are sure that your symbols will hold only real values, you
-would like to have such functions evaluated. Therefore GiNaC allows you to specify
+On the other hand, if you are sure that your symbols will hold only real
+values, you would like to have such functions evaluated. Therefore GiNaC
+allows you to specify
 the domain of the symbol. Instead of @code{symbol x("x");} you can write
 @code{realsymbol x("x");} to tell GiNaC that @code{x} stands in for real values.
 
+@cindex @code{possymbol()}
+Furthermore, it is also possible to declare a symbol as positive. This will,
+for instance, enable the automatic simplification of @code{abs(x)} into 
+@code{x}. This is done by declaying the symbol as @code{possymbol x("x");}.
+
 
 @node Numbers, Constants, Symbols, Basic concepts
 @c    node-name, next, previous, up