 An O("N"5/2log "N") generalization to spherical harmonics on the sphere "S"2 with "N"2 nodes was described by Mohlenkamp, along with an algorithm conjectured (but not proven) to have O("N"2 log2("N")) complexity; Mohlenkamp also provides an implementation in the libftsh library.A spherical-harmonic algorithm with O("N"2log "N") complexity is described by Rokhlin and Tygert.The fast folding algorithm is analogous to the FFT, except that it operates on a series of binned waveforms rather than a series of real or complex scalar values.