Illustration of the Kramers-Kronig relations between a physical (i. e. causal and real) signal and its Fourier transform. The K-K relations in this case require the real and imaginary part thereof are bound by convolution with a Hilbert kernel.
<a href="//commons.wikimedia.org/wiki/User:FDominec" title="User:FDominec">FDominec</a>
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