EXAFS Smoothline Determination Using Splines: Finding the Optimal Smoothline and Fast Computation

Abstract

The feasibility of the PC IMSL cubic spline smoothing routine CSSMH (ICSSCU in the mainframe edition) for numerical determination of the EXAFS smoothline ( μo) is discussed. Examination of the cubic spline algorithm employed suggests that a relatively simple coding modification results in a considerably more efficient algorithm for use in EXAFS. The rudimentatary code already exists in the literature. This allows incorporation of the modified code into current programs without the large memory overhead necessary when IMSL is being used. The degree of flexibility is determined by a parameter which can have values in the range 0 to 1. The EXAFS smoothline requires that the algorithm be used at one extreme end of this range of flexibility. At the other end of this range the routine can be used for interpolation. A suggested path for finding the optimal smoothline, based on the use of coarse and fine smoothing parameters, is discussed.