proj projection

## Syntax

    P = proj(X1,X2)

## Arguments

X1,X2

  two real matrices with equal number of columns

P

  real projection matrix (`P^2=P`)

## Description

`P` is the projection on `X2` parallel to `X1`.

## Examples

    X1=rand(5,2);X2=rand(5,3);
    P=proj(X1,X2);
    norm(P^2-P,1)
    trace(P)    // This is dim(X2)
    [Q,M]=fullrf(P);
    svd([Q,X2])   // span(Q) = span(X2)

## See also

- projspec
- orth
- orthProj
- fullrf