Linear Algebra · Advanced · 5 min

Column space

The column space is the set of all outputs a matrix can produce.

WHAT HAPPENS IF…Can two independent columns span all of three-dimensional space?
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Connect the picture to the ideaA(αβ)=α(1,0,1)+β(0,1,1)A\binom\alpha\beta=\alpha(1,0,1)+\beta(0,1,1)

Every output has coordinates (α,β,α+β), so the image is the plane z=x+y. Its normal is (−1,−1,1). Subtracting the target’s projection onto this normal gives the nearest point in the column space and a residual perpendicular to both columns.

A detail that matters

The column space lives in the output space, while the null space lives in the input space.

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One idea leads to another.

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