ScalingStacks

Lemma 1.2 . [014Z]

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Lemma 1.2.

Given b0,…,bp∈ℕ∗b_{0},\dots,b_{p}\in{\mathbb{N}}^{*}, view

σ={w∈ℝ+p+1∣∑i=0pbi​wi=1}\sigma=\left\{w\in{\mathbb{R}}_{+}^{p+1}\mid\sum_{i=0}^{p}b_{i}w_{i}=1\right\}

as a ℤ{\mathbb{Z}}-simplex. Then bσ=gcd⁡(bi)b_{\sigma}=\gcd(b_{i}), and

Vol⁡(σ)=bσp!​∏ibi.\operatorname{Vol}(\sigma)=\frac{b_{\sigma}}{p!\prod_{i}b_{i}}.

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