Approximation for the exponential integral (Theis well function)
Abstract
In this note, we provide an analytical approximation to the exponential integral valid for all values of its argument. The approximation is constructed by interpolation between the exponential integral's small and large asymptotes. The interpolation contains an unknown function, which is determined using the minimax criterion. The maximum error in the approximation is less than 0.07%, making it useful for routine hydrological applications.
 Publication:

Journal of Hydrology
 Pub Date:
 January 2000
 DOI:
 10.1016/S00221694(99)001845
 Bibcode:
 2000JHyd..227..287B
 Keywords:

 Groundwater;
 Precision;
 Accuracy;
 Computer programs;
 Efficiency;
 Algorithms