ScalingStacks

Example 3.8 . [02KH]

Original official author HTML, exact retained edition. Historical TeX conversion verdicts remain unchanged. Cited-edition alignment and mathematical self-containment are not assessed.

Complete original source context · Original author HTML

Example 3.8.

Let Π\Pi be the polyhedral complex in ℝ3\mathbb{R}^{3} containing the faces of the polyhedra

Λ1={(x1,x2,0)|x1,x2≥0},Λ2={(x1,x2,1)|x1+x2,x1−x2≥0}.\Lambda_{1}=\{(x_{1},x_{2},0)|\,x_{1},x_{2}\geq 0\},\quad\Lambda_{2}=\{(x_{1},x_{2},1)|\,x_{1}+x_{2},x_{1}-x_{2}\geq 0\}.

Then rec⁡(Λ1)\operatorname{rec}(\Lambda_{1}) and rec⁡(Λ2)\operatorname{rec}(\Lambda_{2}) are two cones in ℝ2×{0}\mathbb{R}^{2}\times\{0\} whose intersection is the cone {(x1,x2,0)|x2,x1−x2≥0}\{(x_{1},x_{2},0)|x_{2},x_{1}-x_{2}\geq 0\}. This cone is neither a face of rec⁡(Λ1)\operatorname{rec}(\Lambda_{1}) nor of rec⁡(Λ2)\operatorname{rec}(\Lambda_{2}). Hence rec⁡(Π)\operatorname{rec}(\Pi) is not a complex and, consequently, neither is c⁡(Π)\operatorname{c}(\Pi). In Figure 1 we see the polyhedron Λ1\Lambda_{1} in light grey, the polyhedron Λ2\Lambda_{2} in darker grey and rec⁡(Λ2)\operatorname{rec}(\Lambda_{2}) as dashed lines.

Original mathematics by the credited authors. Source-backed reader collection; mathematical self-containment is not assessed.