  Kontar et al. (2004) have shown how to recover mean source electron spectra
in solar flares through a physical constraint regularization analysis of the
bremsstrahlung photon spectra that they produce. They emphasize the use of
non-square inversion techniques, and preconditioning combined with physical
properties of the spectra to achieve the most meaningful solution to the
problem. Higher-order regularization techniques may be used to generate
${overline F}(E)$ forms with certain desirable properties (e.g., higher order
derivatives). They further note that such analyses may be used to infer
properties of the electron energy spectra at energies well above the maximum
photon energy observed. In this paper we apply these techniques to data from a
solar flare observed by RHESSI on 26 February, 2002. Results using different
orders of regularization are presented and compared for various time intervals.
Clear evidence is presented for a change in the value of the high-energy cutoff
in the mean source electron spectrum with time. We also show how the
construction of the injected (accelerated) electron spectrum $F_0(E_0)$
(assuming that Coulomb collisions in a cold target dominate the electron
energetics) is facilitated by the use of higher-order regularization methods.
