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<H2><A NAME="SECTION00511000000000000000"> </A><A NAME="1694"> </A>
<BR>
Basic Functionality
</H2>
<P>
The basic defining equations for a dynamical system are
entered in the following format:
<P>
<PRE>
# The Lorenz system (lorenz.def)
x' = sigma ( y - x )
y' = rho x - y - x z
z' = -beta z + x y
INITIAL sigma 10 rho 28 beta 2.6667
</PRE>
<P>
We denote the time derivative of a variable by a prime, <TT>'</TT>. This is followed by
an equals sign and then the right hand side. A mapping is input in the
same format using the prime to indicate the new point in phase space.
Variable and parameter names are alphanumeric strings beginning with an
alphabetic character.
Any undefined string is understood to be a parameter in the system.
<P>
Comments are allowed at the end of any line and must
begin with the pound character, #.
As seen in the above example, multiplication is understood,
when no arithmetic operator is present, but it may be
explicitly indicated with an asterisk, *.
The INITIAL declaration assigns initial values to the parameters.
<P>
The parser understands the following fundamental constants, operators, and
special functions:
<P>
<PRE>
constants: PI, pi, E
operators: +, -, *, /, % (mod), ^
special functions: sin, cos, tan, asin, acos, atan, sinh, cosh,
tanh, log, ln, exp, abs, sqrt
</PRE>The special functions all correspond to standard C math library functions.
<P>
If you try this example, set the dynamical system type setting to Vector field, and
then select the ``Build model'' button on the Parser window in order to
create the dynamical system from the text.
<P>
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<ADDRESS>
<I>John Lapeyre</I>
<BR><I>1998-09-04</I>
</ADDRESS>
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