%   function [sigline, logep] = significance(imfs, percenta)
%
%	that is used to obtain the "percenta" line based on Wu and
%	Huang (2004).
%
%   NOTE:   For this program to work well, the minimum data length is 36
%
%   INPUT:
%	    percenta: a parameter having a value between 0.0 ~ 1.0, e.g., 0.05 
%                 represents 95% confidence level (upper bound); and 0.95 
%                 represents 5% confidence level (lower bound) 
%       imfs:     the true IMFs from running EMD code. The first IMF must
%                 be included for it is used to obtain the relative mean
%                 energy for other IMFs. The trend is not included.
%   OUTPUT:
%       sigline:  a two column matrix, with the first column the natural
%                 logarithm of mean period, and the second column the
%                 natural logarithm of mean energy for significance line
%       logep:    a two colum matrix, with the first column the natural
%                 logarithm of mean period, and the second column the
%                 natural logarithm of mean energy for all IMFs
%
% References can be found in the "Reference" section.
%
% The code is prepared by Zhaohua Wu. For questions, please read the "Q&A" section or
% contact
%   zhwu@cola.iges.org
%