Affine transformations and invariants
An invertible affine transformation of ℝⁿ has form T(x)=Ax+b with A invertible.
Key knowledge
An invertible affine transformation of ℝⁿ has form T(x)=Ax+b with A invertible. It preserves affine combinations whose weights sum to one, collinearity, parallelism and the signed parameter along a line. General affine transformations need not preserve Euclidean lengths or angles.
Values and equations
T(Σᵢ wᵢxᵢ)=Σᵢ wᵢT(xᵢ), Σᵢ wᵢ=1
- T
- Invertible affine map x↦Ax+b
- xᵢ
- Finitely many points
- wᵢ
- Real affine weights summing to one; not necessarily nonnegative
Conditions and scope
- Use real finite-dimensional affine coordinates and n≥1; invertibility prevents collapsing lines and preserves noncollinearity.
- For T(x)=Ax+b and U(x)=Cx+d, T∘U(x)=ACx+Ad+b and T⁻¹(y)=A⁻¹(y−b).
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Affine definition and Proposition 4, printed pages 68–69; Theorem 5 and Corollaries 6–8 with proofs, printed pages 69–70. Parallel-line invariance follows by mapping their common direction by A. Proposition 4's displayed composition offsets contain a typo; the correct formula is derived by direct substitution.
2026-10-10 · Independent AI editorial review: All241 compact claims, hypotheses, displayed equations/conventions and all596 origin semantic links read; entire241-entry author exact-source inspection matrix and declared limitations reviewed. Prior105 actual inherited Mathematics/Information records read for whole-inventory breadth. Targeted independent primary sections are listed below; this does NOT claim every cited source body or every proof was independently re-read. This is AI reference-content review, not human disciplinary certification, exhaustive textbook reproduction or experimental replication. Receipt: mathematics-information-independent-content-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- math-affine-transformations-invariants
- Revision
- university-core.1
- Structured reference record
- University core expansion