Unrestricted algorithms for elementary and special functions
52. R. P. Brent,
Unrestricted algorithms for elementary and special functions,
in Information Processing 80 (edited by S. H. Lavington),
North-Holland, Amsterdam, 1980, 613-619.
Retyped with minor corrections 1999.
We describe some "unrestricted" algorithms which are useful for the
computation of elementary and special functions when the precision
required is not known in advance. Several general classes of algorithms
are identified and illustrated by examples.
The topics include:
power series methods,
use of halving identities,
numerical contour integration,
and the arithmetic-geometric mean.
Most of the algorithms discussed are implemented in the
For related work see Brent
Errata for original version
Page 615, remove the absolute value signs in
equation (13) and the following paragraph (x should be large
and positive here).
Page 616, second half of equation (26):
insert a minus sign after the equals sign.
Page 617, equation (39):
delete " / j ! ".
Page 617, equation (42):
the assumption "j < k" should be added. Also, the
contour C needs to be enlarged slightly.
Page 617, left-hand-side of equation (44):
replace "Sj,k" by "S2j,k".
Page 617, ten lines after equation (44):
replace "O(jn2)" by "O(j2n)".
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