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# Orthogonal intrinsic mode functions via optimization approach

• * Corresponding author: Bingo Wing-Kuen Ling

The first author is supported by NSF grant xx-xxxx

• This paper proposes an optimization approach to find a set of orthogonal intrinsic mode functions (IMFs). In particular, an optimization problem is formulated in such a way that the total energy of the difference between the original IMFs and the corresponding obtained IMFs is minimized subject to both the orthogonal condition and the IMF conditions. This formulated optimization problem consists of an exclusive or constraint. This exclusive or constraint is further reformulated to an inequality constraint. Using the Lagrange multiplier approach, it is required to solve a linear matrix equation, a quadratic matrix equation and a highly nonlinear matrix equation only dependent on the orthogonal IMFs as well as a nonlinear matrix equation dependent on both the orthogonal IMFs and the Lagrange multipliers. To solve these matrix equations, the first three equations are considered. First, a new optimization problem is formulated in such a way that the error energy of the highly nonlinear matrix equation is minimized subject to the linear matrix equation and the quadratic matrix equation. By finding the nearly global optimal solution of this newly formulated optimization problem and checking whether the objective functional value evaluated at the obtained solution is close to zero or not, the orthogonal IMFs are found. Finally, by substituting the obtained orthogonal IMFs to the last matrix equation, this last matrix equation reduced to a linear matrix equation which is only dependent on the Lagrange multipliers. Therefore, the Lagrange multipliers can be found. Consequently, the solution of the original optimization problem is found. By repeating these procedures with different initial conditions, a nearly global optimal solution is obtained.

Mathematics Subject Classification: Primary: 58F15, 58F17; Secondary: 53C35.

 Citation: • • Figure 1.  Original signal

Figure 2.  Signal components

Figure 3.  Normalized IMFs

Figure 4.  Components obtained by the Gram Schmidt orthogonalization method

Figure 5.  Components obtained by our proposed method

Table 1.  Orthogonal errors of all the IMFs $err_{orth}$

 Signal Our proposed method Gram Schmidt orthogonalization method  Normalization method $x(t)=\sin (2 \pi t) e^{-\frac{t^{2}}{2}}$$+e^{-t} \cos (2 \pi t) 0 0 1.3545 Table 2. Errors between the total number of the extrema and the total number of the zero crossing points of all the IMFs err_{ex_-zx}  Signal Our proposed method Gram Schmidt orthogonalization method  Normalization method x(t)=\sin (2 \pi t) e^{-\frac{t^{2}}{2}}$$+e^{-t} \cos (2 \pi t)$ 0 25 0

Table 3.  Errors between the total number of the extrema and the total number of the zero crossing points of all the IMFs $err_{ex_-zx}$

 Signal Our proposed method Gram Schmidt orthogonalization method  Normalization method $x(t)=\sin (2 \pi t) e^{-\frac{t^{2}}{2}}$$+e^{-t} \cos (2 \pi t)$ $0.9139\times10^{-4}$ $0.9801\times10^{-4}$ $0.6368\times10^{-4}$
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Tables(3)

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