We prove or derive the following:
l4"">href=""/science?_ob=MathURL&_method=retrieve&_udi=B6TYH-4HDG9G6-6&_mathId=mml4&_user=10&_cdi=5619&_rdoc=19&_handle=V-WA-A-W-WV-MsSWYVW-UUW-U-AAZCBWVUDD-AAZWEUVYDD-VBCEUVVD-WV-U&_acct=C000050221&_version=1&_userid=10&md5=d344d995a410862f5bf7ff33002f24a8"" title=""Click to view the MathML source"">• The correct dimensionless groups. Erdélyi's expansion is properly expressed in terms of scaled coefficients .
href=""/science?_ob=MathURL&_method=retrieve&_udi=B6TYH-4HDG9G6-6&_mathId=mml6&_user=10&_cdi=5619&_rdoc=19&_handle=V-WA-A-W-WV-MsSWYVW-UUW-U-AAZCBWVUDD-AAZWEUVYDD-VBCEUVVD-WV-U&_acct=C000050221&_version=1&_userid=10&md5=f403cab2def9a99859d5fa4ae7683a5d"" title=""Click to view the MathML source"">• Two explicit expressions for in terms of combinatorial objects called partial ordinary Bell polynomials. This form is probably computationally optimal and makes checking for correctness a relatively straightforward process.
href=""/science?_ob=MathURL&_method=retrieve&_udi=B6TYH-4HDG9G6-6&_mathId=mml8&_user=10&_cdi=5619&_rdoc=19&_handle=V-WA-A-W-WV-MsSWYVW-UUW-U-AAZCBWVUDD-AAZWEUVYDD-VBCEUVVD-WV-U&_acct=C000050221&_version=1&_userid=10&md5=8436029b6a99c59ce4b77d2dab6242cc"" title=""Click to view the MathML source"">• A recursive expression for .
href=""/science?_ob=MathURL&_method=retrieve&_udi=B6TYH-4HDG9G6-6&_mathId=mml10&_user=10&_cdi=5619&_rdoc=19&_handle=V-WA-A-W-WV-MsSWYVW-UUW-U-AAZCBWVUDD-AAZWEUVYDD-VBCEUVVD-WV-U&_acct=C000050221&_version=1&_userid=10&md5=3f27b001bf4aa98e342e97f1d3d8ae55"" title=""Click to view the MathML source"">• Each coefficient can be expressed as a polynomial in href=""/science?_ob=MathURL&_method=retrieve&_udi=B6TYH-4HDG9G6-6&_mathId=mml12&_user=10&_cdi=5619&_rdoc=19&_handle=V-WA-A-W-WV-MsSWYVW-UUW-U-AAZCBWVUDD-AAZWEUVYDD-VBCEUVVD-WV-U&_acct=C000050221&_version=1&_userid=10&md5=8690343704de6f9061a108d0a312549b"" title=""Click to view the MathML source"">(α+s)/μ, where href=""/science?_ob=MathURL&_method=retrieve&_udi=B6TYH-4HDG9G6-6&_mathId=mml13&_user=10&_cdi=5619&_rdoc=19&_handle=V-WA-A-W-WV-MsSWYVW-UUW-U-AAZCBWVUDD-AAZWEUVYDD-VBCEUVVD-WV-U&_acct=C000050221&_version=1&_userid=10&md5=6778eead44863d6452a1fc2542e7c358"" title=""Click to view the MathML source"">α and href=""/science?_ob=MathURL&_method=retrieve&_udi=B6TYH-4HDG9G6-6&_mathId=mml14&_user=10&_cdi=5619&_rdoc=19&_handle=V-WA-A-W-WV-MsSWYVW-UUW-U-AAZCBWVUDD-AAZWEUVYDD-VBCEUVVD-WV-U&_acct=C000050221&_version=1&_userid=10&md5=b9687a733ab7be6c635e893325df7bd6"" title=""Click to view the MathML source"">μ are quantities in Erdélyi's formulation.
The main insight that emerges is that the traditional approach to Laplace's method, involving reversion of a series, is less efficient and need only be invoked if one is interested in the role of the reversion coefficients in Erdélyi's expansion—a point which Erdélyi himself alluded to.
We consider as an example an integral that occurs in a variational approach to finding the binding energy of helium dimers. We also present a three-line computer code to generate the coefficients exactly in the general case. In a sequel paper (to be published in SIAM Review), a new representation for the gamma function is obtained, and the link with Faà di Bruno's formula is explained.