The general R-stage implicit Runge-Kutta method is defined by
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(6.1) |
where

with
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(6.2) |
and
,  |
(6.3) |
The functions are no longer defined explicitly but by a set of implicit equations and thus making the derivation of such methods tedious. We shall consider here only the two-stage method obtained by setting in (6.1)-(6.3). Let us also recall the expansion for which is given by
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(6.4) |
where, extending the notation of (3.18)


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