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cmorwavf

Complex Morlet wavelet

    Description

    [psi,x] = cmorwavf(lb,ub,n) returns the complex Morlet wavelet, psi, with time-decay parameter, fb, and center frequency, fc, both equal to 1. The wavelet is evaluated on an n-point regular grid, x, for the interval [lb,ub]. The general expression for the complex Morlet wavelet is

    ψ(x)=1πfbexp(2πifcx)exp(x2/fb).

    example

    [psi,x] = cmorwavf(lb,ub,n,fb,fc) returns the complex Morlet wavelet with time-decay parameter, fb, and center frequency, fc.

    Examples

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    Construct a complex-valued Morlet wavelet with a bandwidth parameter of 1.5 and a center frequency of 1. Set the effective support to [-8,8] and the length of the wavelet to 1000.

    N = 1000;
    Lb = -8;
    Ub = 8;
    fb = 1.5;
    fc = 1;
    [psi,x] = cmorwavf(Lb,Ub,N,fb,fc);

    Plot the real and imaginary parts of the wavelet.

    subplot(2,1,1)
    plot(x,real(psi)); title('Real Part');
    subplot(2,1,2)
    plot(x,imag(psi)); title('Imaginary Part');

    Figure contains 2 axes. Axes 1 with title Real Part contains an object of type line. Axes 2 with title Imaginary Part contains an object of type line.

    This example shows how the complex Morlet wavelet shape in the frequency domain is affected by the value of the bandwidth parameter (Fb). Both wavelets have a center frequency of 1. One wavelet has an Fb value of 0.5 and the other wavelet has a value of 8.

    f = -5:.01:5;  
    Fc = 1;  
    Fb1 = 0.5;  
    Fb2 = 8;  
    psihat1 = exp(-pi^2*Fb1*(f-Fc).^2);  
    psihat2 = exp(-pi^2*Fb2*(f-Fc).^2);  
    plot(f,psihat1)  
    hold on;  
    plot(f,psihat2,'r')  
    legend('Fb = 0.5','Fb = 8')

    Figure contains an axes. The axes contains 2 objects of type line. These objects represent Fb = 0.5, Fb = 8.

    The Fb bandwidth parameter for the complex Morlet wavelet is the inverse of the variance in frequency. Therefore, increasing Fb results in a narrower concentration of energy around the center frequency.

    Input Arguments

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    Left endpoint of the closed interval, specified as a scalar. lb is strictly less than ub.

    Right endpoint of the closed interval, specified as a scalar. ub is strictly greater than ub.

    Number of regularly spaced points in the interval [lb,ub], specified as a positive integer.

    Time-decay parameter, specified as a positive scalar. fb controls the decay in the time domain and the corresponding energy spread (bandwidth) in the frequency domain. fb is the inverse of the variance in the frequency domain.

    • Increasing fb makes the wavelet energy more concentrated around the center frequency and results in slower decay of the wavelet in the time domain.

    • Decreasing fb results in faster decay of the wavelet in the time domain and less energy spread in the frequency domain.

    The value of fb does not affect the center frequency. When converting from scale to frequency, only the center frequency affects the frequency values. The energy spread or bandwidth parameter affects how localized the wavelet is in the frequency domain.

    Center frequency, specified as a positive scalar.

    Output Arguments

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    Complex Morlet wavelet, returned as a complex-valued 1-by-n vector.

    Sample points where the complex Morlet vector is evaluated, returned as a 1-by-n vector. The sample points are evenly distributed between lb and ub.

    References

    [1] Teolis, Anthony. Computational Signal Processing with Wavelets. Boston, MA: Birkhäuser Boston, 1998. https://doi.org/10.1007/978-1-4612-4142-3.

    See Also

    Introduced before R2006a