ScalingStacks

Proof. [02SJ]

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Proof.

The H-representation of c⁡(ψ)\operatorname{c}(\psi) is

dom⁡(c⁡(ψ))\displaystyle{\operatorname{dom}}(\operatorname{c}(\psi)) ={(u,r)∈N~ℝ∣r≥0},\displaystyle=\{(u,r)\in{\widetilde{N}}_{\mathbb{R}}\mid r\geq 0\},
c⁡(ψ)​(u,r)\displaystyle\operatorname{c}(\psi)(u,r) =minΛ⁡(mΛ​(u)+lΛ​r).\displaystyle=\min_{\Lambda}(m_{\Lambda}(u)+l_{\Lambda}r).

By Proposition 3.64

stab⁡(c⁡(ψ))=ℝ≥0​(0,1)+conv⁡({(mΛ,lΛ)}Λ∈Π).\operatorname{stab}(\operatorname{c}(\psi))=\mathbb{R}_{\geq 0}(0,1)+\operatorname{conv}(\{(m_{\Lambda},l_{\Lambda})\}_{\Lambda\in\Pi}).

Furthermore, by the same proposition, for x∈stab⁡(ψ)x\in\operatorname{stab}(\psi),

ψ∨(x)=sup{∑Λ−λΛlΛ|λΛ≥0,∑ΛλΛ=1,∑ΛλΛmΛ=x}.\psi^{\vee}(x)=\sup\left\{\sum_{\Lambda}-\lambda_{\Lambda}l_{\Lambda}\bigg|\lambda_{\Lambda}\geq 0,\sum_{\Lambda}\lambda_{\Lambda}=1,\sum_{\Lambda}\lambda_{\Lambda}m_{\Lambda}=x\right\}.

Hence epi⁡(−ψ∨)=ℝ≥0​(0,1)+conv⁡({(mΛ,lΛ)}Λ∈Π),\operatorname{epi}(-\psi^{\vee})=\mathbb{R}_{\geq 0}(0,1)+\operatorname{conv}(\{(m_{\Lambda},l_{\Lambda})\}_{\Lambda\in\Pi}), which proves the statement. ∎

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