<A NAME=EQUATION>
<TITLE>EQUATION</TITLE></A>
<b><a href=r37_idx.html>INDEX</a></b><p><p>
<B>EQUATION</B> _ _ _ _ _ _ _ _ _ _ _ _ <B>type</B><P>
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An <em>equation</em> is an expression where two algebraic expressions
are connected by the (infix) operator
<A HREF=r37_0110.html>equal</A> or by <em>=</em>.
For access to the components of an <em>equation</em> the operators
<A HREF=r37_0158.html>lhs</A>,
<A HREF=r37_0175.html>rhs</A> or
<A HREF=r37_0169.html>part</A> can be used. The
evaluation of the left-hand side of an <em>equation</em> is controlled
by the switch
<A HREF=r37_0283.html>evallhseqp</A>, while the right-hand side is
evaluated unconditionally. When an <em>equation</em> is part of a
logical expression, e.g. in a
<A HREF=r37_0052.html>if</A> or
<A HREF=r37_0228.html>while</A> statement,
the equation is evaluated by subtracting both sides can comparing
the result with zero.
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Equations occur in many contexts, e.g. as arguments of the
<A HREF=r37_0182.html>sub</A>
operator and in the arguments and the results
of the operator
<A HREF=r37_0179.html>solve</A>. An equation can be member of a
<A HREF=r37_0302.html>list</A>
and you may assign an equation to a variable. Elementary arithmetic is supported
for equations: if
<A HREF=r37_0283.html>evallhseqp</A> is on, you may add and subtract
equations, and you can combine an equation with a scalar expression by
addition, subtraction, multiplication, division and raise an equation
to a power.
<P> <H3>
examples: </H3>
<P><PRE><TT>
on evallhseqp;
u:=x+y=1$
v:=2x-y=0$
2*u-v;
- 3*y=-2
ws/3;
2
y=--
3
</TT></PRE><P><P>
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Important: the equation must occur in the leftmost term of such an expression.
For other operations, e.g. taking function values of both sides, use the
<A HREF=r37_0163.html>map</A> operator.
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