Projection onto Linearly Dependent Vectors
Now consider another example:
The projections of onto these vectors are
The sum of the projections is
Something went wrong, but what? It turns out that a set of vectors can be used to reconstruct an arbitrary vector in from its projections only if they are linearly independent. In general, a set of vectors is linearly independent if none of them can be expressed as a linear combination of the others in the set. What this means intuitively is that they must ``point in different directions'' in -space. In this example so that they lie along the same line in -space. As a result, they are linearly dependent: one is a linear combination of the other ( ).
Projection onto Non-Orthogonal Vectors