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Is there an interpretation of $X^{\dagger}Y$ in terms of a projection or a least-squares formulation? Note that $\dagger$ denotes the pseudo-inverse and $X$ is a square matrix, and $Y$ is a rectangular matrix and the entries in both are real-valued. Am trying to have a better interpretation of the pseudo-inverse in this situation.

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Is $Y$ a vector? –  littleO Nov 14 '12 at 21:28
    
Its a rectangular Matrix! –  qlinck Nov 14 '12 at 21:49
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1 Answer

up vote 3 down vote accepted

What does the pseudoinverse of $A$ do? It takes a vector $b$ as input, and returns as output the vector $x$ of least 2-norm such that $Ax = \hat{b}$, where $\hat{b}$ is the projection of $b$ onto the column space of $A$.

Strang's book Linear Algebra and Its Applications has a good presentation of this topic.

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