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I was recently reading about Fourier dimension of Boolean functions. What I understand is that if we take the Fourier expansion of $f: \{\pm1\}^n \to \{\pm1\}$ and consider the monomials with non zero Fourier coefficients as vectors in $\mathbb{F}_2^n$, then the Fourier dimension is the dimension of the span of these vectors.

This might help to understand when a Boolean function is "reduceable" or "equivalent" to another one. For example, if we replace a variable with a product of say $m$ variables, then in the vectors of the corresponding monomials, those $m$ places will be $1$ or $0$ together. This gives us that the Fourier dimension remains unchanged in such a transformation.

My question is for what kind of variable transformations does the Fourier dimension remain unchanged?

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  • $\begingroup$ It's probably linear-invariant or even affine-invariant. $\endgroup$ May 12, 2022 at 5:20
  • $\begingroup$ @YuvalFilmus would it be invariant under product or composition of $f$ with itself? $\endgroup$ May 14, 2022 at 7:26
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    $\begingroup$ Why not check it using some examples? $\endgroup$ May 14, 2022 at 10:20

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