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The $p$-Wasserstein between two measures $\nu_1$ and $\nu_2$ on $X$ is given by

$$W^p_p(\nu_{1},\nu_{2})=\underset{\pi\in\Gamma(\nu_{1},\nu_{2})}{\inf}\int_{\mathbf{\mathcal{X}}^{2}}d(x,y)^p\pi(dx,dy)$$

where $\Gamma(\nu_{1},\nu_{2})$ is the set of all couplings between $\nu_1$ and $\nu_2$. For $X=\mathbb{R}^d$ and $d$ being the Euclidean distance the optimal transport between $\nu_{1}=N(m,V)$ and $\nu_{2}=N(n,U)$ is well known for $p=2$, see Givens and Shortt. On the other hand $W_1$ has stronger Kantorovich duality. So my question is: is there a chance that both things are basically the same and we can have the best of both worlds?

More precisely: does there exist a constant $C > 0$ such that for any dimension $d$, $m = 0, n = 0$ and any $U, V$ we have
$$\frac{W_2(\nu_{1},\nu_{2})}{W_1(\nu_{1},\nu_{2})} \le C?$$ I assume that there is a counterexample but I checked the dimension $1$ and here it's fine. Also this question is a mod of an old one.

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  • $\begingroup$ two quick questions: 1) do you really want the constant $C$ to be uniform in the dimension (you wrote it pretty explicitly, just checking) 2) the $W_p$ distances also enjoy a Kantorovich duality, so what's so special here about $p=1$? $\endgroup$ Commented Mar 25 at 23:17
  • $\begingroup$ @leomonsaingeon Hi Leo! I asked this question mostly out of curiosity there no specific app. Also my current project is the first one dealing with duality for Wassersteins. So do not expect much wisdom in details of my question. (1) The reasons to put a constant independent of dimensions are (a) I wanted to avoid arguments by compactness (if there are any) and (b) In AI apps which I'm exposed to, dimensions are large, so if the constant grows fast with dimension that's no good. (2)For $W_1$ we have Theorem 1.14 in Villani's "Topics in optimal transportation", may be useful I guess. $\endgroup$ Commented Mar 27 at 3:55

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