On Sat, Jun 6, 2009 at 14:59, Alan G Isaac <ais...@american.edu> wrote: > On 6/6/2009 2:58 PM Charles R Harris apparently wrote: >> How about the common expression >> exp((v.t*A*v)/2) >> do you expect a matrix exponential here? > > > I take your point that there are conveniences > to treating a 1 by 1 matrix as a scalar. > Most matrix programming languages do this, I think. > For sure GAUSS does. The result of x' * A * x > is a "matrix" (it has one row and one column) but > it functions like a scalar (and even more, > since right multiplication by it is also allowed). > > While I think this is "wrong", especially in a > language that readily distinguishes scalars > and matrices, I recognize that many others have > found the behavior useful. And I confess that > when I talk about quadratic forms, I do treat > x.T * A * x as if it were scalar.
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 -- 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
