[Merged by Bors] - feat(CategoryTheory/Adjunction/Additive): adjunctions between additive functors

[smorel394]

This provides some results and constructions for adjunctions between functors on preadditive categories:

• If one of the adjoint functors is additive, so is the other.
• If one of the adjoint functors is additive, the equivalence Adjunction.homEquiv lifts to
  an additive equivalence Adjunction.homAddEquiv.
• We also give a version of this additive equivalence as an isomorphism of preadditiveYoneda
  functors (analogous to Adjunction.compYonedaIso), in
  Adjunction.compPreadditiveYonedaIso.

---

[github-actions]

PR summary 6d70f2e362

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference
Mathlib.CategoryTheory.Adjunction.Additive (new file)	808

---

Declarations diff

+ compPreadditiveYonedaIso
+ compPreadditiveYonedaIso_hom_app_app_apply
+ compPreadditiveYonedaIso_inv_app_app_apply
+ homAddEquiv
+ homAddEquiv_add
+ homAddEquiv_apply
+ homAddEquiv_neg
+ homAddEquiv_sub
+ homAddEquiv_symm_add
+ homAddEquiv_symm_apply
+ homAddEquiv_symm_neg
+ homAddEquiv_symm_sub
+ homAddEquiv_symm_zero
+ homAddEquiv_zero
+ left_adjoint_additive
+ right_adjoint_additive

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.

---

No changes to technical debt.

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[joelriou]

Could you also edit the PR description so as to take into account the changes.

[smorel394]

Could you also edit the PR description so as to take into account the changes.

Done.

[joelriou]

Thanks!

bors merge

[mathlib-bors]

Pull request successfully merged into master.

Build succeeded:

• Build
• Lint style