On Sat, Jun 6, 2009 at 16:00, Alan G Isaac <ais...@american.edu> wrote: > On 6/6/2009 4:30 PM Robert Kern apparently wrote: >> The old idea of introducing RowVector and ColumnVector would help >> here. If x were a ColumnVector and A a Matrix, then you can introduce >> the following rules: >> >> x.T is a RowVector >> RowVector * ColumnVector is a scalar >> RowVector * Matrix is a RowVector >> Matrix * ColumnVector is a ColumnVector > > > To me, a "row vector" is just a matrix with a single row, > and a "column vector" is just a matrix with a single column. > Calling them "vectors" is rather redundant, since matrices > are also vectors (i.e., belong to a vector space). > > I think the core of the row-vector/column-vector proposal > is really the idea that we could have 1d objects that > also have an "orientation" for the purposes of certain > operations. But then why not just use matrices, which > automatically provide that "orientation"?
Because (x.T * x) where x is an (n,1) matrix and * is matrix multiplication (i.e. MM(n,1) -> MM(1,1)) is not the same thing as the inner product of a vector (RR^n -> RR). Please see the post I was responding to for the motivation. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
