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Automatic Generation of Taylor Coefficients

The algorithm for computing Taylor coefficients recursively has been known since the 60s and is commonly referenced as automatic differentiation in the literature. It has been employed in software packages such as ATOFMT. A detailed description of the algorithm can be found in [1] (see more references therein). Here we give a brief account of the idea involved.

Let f(t) be an analytic function and denote the ith Taylor coefficient at tex2html_wrap_inline607 by

eqnarray321

where tex2html_wrap_inline625 is the ith derivative of f at tex2html_wrap_inline607 . The Taylor expansion of f(t) around tex2html_wrap_inline607 can be conveniently expressed as

eqnarray326

Let tex2html_wrap_inline637 be the ith Taylor coefficients of p, q at tex2html_wrap_inline607 . The Taylor coefficients for tex2html_wrap_inline645 , pq and p/q can be obtained recursively using the following rules.

  eqnarray328

To compute the Taylor coefficients for (1), one first decomposes the right hand side of the differential equation into a series of simple expressions by introducing new variables, such that each expression involves only one arithmetic operation. These expressions are commonly called code lists. One then uses the recursive relations (5) and the initial values to generate the Taylor coefficients for all the the variables.

For example, the Van der Pol equation (3) can be decomposed as

eqnarray344

Using the initial value tex2html_wrap_inline651 , the Taylor coefficients of all tex2html_wrap_inline653 s can be easily generated using (5).

The Taylor coefficients for elementary functions can also be generated recursively. Some of the rules are:

eqnarray347

eqnarray355

eqnarray366

eqnarray378



Maorong Zou
Tue Nov 13 09:42:48 CST 2001