ScalingStacks

Remark 5.8 . [02SZ]

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Remark 5.8.

In case we are given a strictly concave support function Ψ\Psi on a fan Σ\Sigma, then NΣN_{\Sigma} is homeomorphic to the polytope ΔΨ\Delta_{\Psi} introduced in §4.4. An homeomorphism is obtained as the composition of 𝐞K{\operatorname{\mathbf{e}}}_{K} with the moment map μ:XΣ​(ℝ≥0)→ΔΨ\mu\colon X_{\Sigma}(\mathbb{R}_{\geq 0})\rightarrow\Delta_{\Psi} induced by Ψ\Psi:

NΣ⟶𝐞KXΣ​(ℝ≥0)⟶μΔΨu⟼𝐞K⁡(u)⟼∑exp⁡(−λK​⟨m,u⟩)​m∑exp⁡(−λK​⟨m,u⟩)\begin{matrix}N_{\Sigma}&\mathrel{\mathop{\kern 0.0pt\longrightarrow}\limits^{{\operatorname{\mathbf{e}}}_{K}}}&X_{\Sigma}(\mathbb{R}_{\geq 0})&\mathrel{\mathop{\kern 0.0pt\longrightarrow}\limits^{\mu}}&\Delta_{\Psi}\\[5.69054pt] u&\longmapsto&{\operatorname{\mathbf{e}}}_{K}(u)&\longmapsto&\frac{\sum\exp(-\lambda_{K}\langle m,u\rangle)m}{\sum\exp(-\lambda_{K}\langle m,u\rangle)}\end{matrix}

where the sums in the last expression are over the elements m∈M∩ΔΨm\in M\cap\Delta_{\Psi}.

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