January 2000
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Advances in Imaging and Electron Physics
The direct numerical evaluation of Eq.(2.4-45) by computer runs into difficulties. To recognize the reason we list in Tables 6.1-1 typical values of λ1, λ2, λp1, and λp2. The magnitude of λl and λ2 lies between 1 and 2.51 x 10-3 for p ≥ 0.05 but the magnitude of c pλp1 for ŋ in the range from 1 to 100 and c p = 1.98 x 10-12 is in the order of 10-14 to 10-19 and c pλp2 is even smaller except when p is very close to 0.5. The computer must produce small differences of numbers of the order of 1020, which requires too much precision. Our way around this difficulty uses a series expansion in powers of c p.