Hermitian function
In mathematical analysis, a Hermitian function is a complex function with the property that its complex conjugate is equal to the original function with the variable changed in sign:
for all in the domain of. In physics, this property is referred to as PT symmetry.
This definition extends also to functions of two or more variables, e.g., in the case that is a function of two variables it is Hermitian if
for all pairs in the domain of.
From this definition it follows immediately that: is a Hermitian function if and only if
Hermitian functions appear frequently in mathematics, physics, and signal processing. For example, the following two statements follow from basic properties of the Fourier transform:
- The function is real-valued if and only if the Fourier transform of is Hermitian.
- The function is Hermitian if and only if the Fourier transform of is real-valued.
Since the Fourier transform of a real signal is guaranteed to be Hermitian, it can be compressed using the Hermitian even/odd symmetry. This, for example, allows the discrete Fourier transform of a signal to be stored in the same space as the original real signal.
Where the is cross-correlation, and is convolution.
- If both f and g are Hermitian, then.
