ScalingStacks

3.4 [0358]

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3.4

Let (๐’ž,m)({\mathscr{C}},m) be a weighted integral โ„{\mathbb{R}}-affine polyhedral complex of pure dimension nn. For ฮฑโˆˆAcn,nโ€‹(๐’ž)\alpha\in A_{c}^{n,n}({\mathscr{C}}), we set

โˆซ(๐’ž,m)ฮฑ:=โˆ‘ฯƒโˆˆ๐’žnmฯƒโ€‹โˆซฯƒฮฑ,\int_{({\mathscr{C}},m)}\alpha:=\sum_{\sigma\in{\mathscr{C}}_{n}}m_{\sigma}\int_{\sigma}\alpha,

where we use integration from 2.4 on the right. We define integrals over the boundary of ๐’ž{\mathscr{C}} for a superform ฮฒ\beta in Acnโˆ’1,nโ€‹(๐’ž)A_{c}^{n-1,n}({\mathscr{C}}) or in Acn,nโˆ’1โ€‹(๐’ž)A_{c}^{n,n-1}({\mathscr{C}}) by

โˆซโˆ‚(๐’ž,m)ฮฒ=โˆ‘ฯƒโˆˆ๐’žnmฯƒโ€‹โˆซโˆ‚ฯƒฮฒ,\int_{\partial({\mathscr{C}},m)}\beta=\sum_{\sigma\in{\mathscr{C}}_{n}}m_{\sigma}\int_{\partial\sigma}\beta,

where we use the boundary integrals from 2.8 on the right. Note that the boundary โˆ‚๐’ž\partial{\mathscr{C}} may be defined as the subcomplex consisting of the polyhedra of dimension at most nโˆ’1n-1, but there is no canonical weight on โˆ‚๐’ž\partial{\mathscr{C}}. Indeed, the boundary integral โˆซโˆ‚(๐’ž,m)ฮฒ\int_{\partial({\mathscr{C}},m)}\beta depends on the relative situation โˆ‚๐’žโŠ‚๐’ž\partial{\mathscr{C}}\subset{\mathscr{C}} because of the weight mฯƒm_{\sigma} and the contraction with respect to the vectors ฯ‰ฯ,ฯƒ\omega_{\rho,\sigma} used in the definitions. This is similar to the situation in real analysis where boundary integrals depend on the relative orientation. These classical boundary integrals do depend only on the restriction of the differential form to the boundary which is clearly wrong for our boundary integrals. However, it is still true that โˆซโˆ‚(๐’ž,m)ฮฒ=0\int_{\partial({\mathscr{C}},m)}\beta=0 if the support of ฮฒ\beta is disjoint from โˆ‚๐’ž\partial{\mathscr{C}}.

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