Discrete Fourier Transform Low/High Pass Filter.

This is a simply implement of Discrete Fourier Transform Low/High Pass Filter for 1-D data.

% function [g] = FFTPF1D (X,binsize, f, P)
% Discrete Fourier Transform Low/High Pass Filter.
% This is a simply implement of such a filter for a given 1-D data.
% X: the array of you data, each data point is a bin of signal
% binsize: the bin size in your data data
% f: the cutoff of wave length,
% P: 1, or 0, true or false : true, low pass, which eliminating higher
% than f frequence signals, false, high pass, which eliminating lower
% than f frequence signals.
% It could be easily modified into 2-D version, or translated into
% R/S-language.
% Example:
% a=1:2:1000;
% b=sin(a) + sin(2.*a) + sin(0.1 .* a) + ...
% c=FFTPF1D(b, 2, 10, 1)
% Author: Zhihua Zhang. [e-mail]
% Feel free to use and distribute this code for training or
% academic propose.