Gaussian Elimination and Row Reduction: Examples and Counterexamples
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1 · Prerequisites
Abstract Algebra
Linear Algebra
Number Theory
Real Analysis
2 · Logical flowchart
3 · Items
Example
A 3×3 system row reduces to a unique solution
Example
A 3×3 system has no solution because its augmented column contains a pivot
Example
A consistent underdetermined system has an affine two-parameter solution set
Example
A 3×3 inverse computed by row reducing [A∣ I]
Example
One matrix has two distinct row echelon forms but one reduced row echelon form
Example
The rank and solution behaviour of a parameterised matrix change at one exceptional parameter
Example
An invertible 3×3 real matrix factored explicitly into elementary matrices
Counterexample
Row-equivalent matrices can have different column spaces even though their column ranks agree
Counterexample
Over F₂, the equation x+y=0 has exactly two solutions, so the infinite-field hypothesis is necessary
Sources
- D. Margalit and J. Rabinoff, Interactive Linear Algebra, §§1.2–1.3
- D. Margalit and J. Rabinoff, Interactive Linear Algebra, §1.3
- D. Margalit and J. Rabinoff, Interactive Linear Algebra, §2.4
- D. Margalit and J. Rabinoff, Interactive Linear Algebra, §3.6
- J. Hefferon, Linear Algebra, 4th ed., Ch. One, §III.2
- J. Hefferon, Linear Algebra, 4th ed., Ch. One, exercises after §III.2
- J. Hefferon, Linear Algebra, 4th ed., Ch. Three, §IV.3
- J. Hefferon, Linear Algebra, 4th ed., Ch. Three, Remark 3.15