Algorithm 1 The sifting algorithm for empirical mode decomposition (EMD).
1:	Find the locations of all the extrema of x(k);
2:	Interpolate (via spline interpolation) between all of the minima (respectively maxima) to obtain the signal envelope passing through the minima, emin(k) (resp. emax(k));
3:	Calculate the local mean m(k) = (emin(k) + emax(k))/2;
4:	Subtract the local mean from the signal to obtain the ‘oscillating’ signal d(k) = x(k) − m(k);
5:	If the resulting signal d(k) obeys the stopping criterion, it becomes the first IMF; otherwise, set x(k) = d(k) and repeat the process from Step 1 until the first IMF is obtained.