Add Butterworth filter option to FFTSmooth

[Dennis Mikkelson]

A Butterworth filter option can be easily added to FFTSmooth so that noisy data can be smoothed without introducing the "ringing" artifacts caused by an abrupt frequency cutoff as is done by the "Zeroing" option. This will require two positive integer parameters, a cutoff control parameter, n, and the order of the filter.

[Dennis Mikkelson]

(In [5658]) This second version of FFTSmooth adds an arbitrary order "Butterworth" filter in addition to the original "Zeroing" option. The Butterworth filter takes two additional positive integer parameters, "n" and the "order" of the filter, in a character string. The interpretation of "n" is as in the "Zeroing" case, however, in keeping with the documentation. n MUST be strictly more than 1 for both the Butterworth and the Zeroing options, in this version. refs #1477

[Dennis Mikkelson]

This option has been added as a second version of FFTSmooth, in files FFTSmooth2.h and FFTSmooth2.cpp

[Dennis Mikkelson]

(In [5667]) "Gold" test result files for Zeroing and Butterworth filter options for the FFTSmooth2 algorithm. refs #1477

[Dennis Mikkelson]

(In [5668]) Test code for both Zeroing and Butterworth filter options for the second version of FFTSmooth, in class FFTSmooth2. refs #1477

[Nick Draper]

fill in missing resolution

[Vickie Lynch]

Tested FFTSmoooth with Butterworth filter on discontinuous data and results were good.

[Stuart Campbell]

This ticket has been transferred to github issue ​2324