Simple Matrix Manipulation Extressions

[John W. Eaton]

On  8-Nov-1997, john <address@hidden> wrote:

|       Are there any simple expressions for these octave expressions:
| In each case I introduce loops, multiplications or something a bit
| horrible to achieve something fairly simple.
| 
| 1. given matrix A and row vector V , add V to every row of A
| 
|         A + ones(rows(A),1) * V
| 
| 2. similar problem for multiply:
| 
|         A * diag(V)
|     or  A .* ones(rows(A),1) * V

Some future version of Octave will probably allow things like

  A .+ V

and

  A .* V

to do what you expect.  For now, you have to use a multiplication or
indexing tricks to convert the vector to a matrix of the proper size.

| 3. given a matrix A and a scalar s, take the minimum of an element of the
|    matrix and the scalar.
| 
|         (A < s) .* A + (s <= A) .* s)

min (A, s)

| 4. given two same sized matrices A, B, find the pair-wise minimum of each 
|    element:
|         (A < B) .* A + (A >= B) .* B

min (A, B)

I don't know of better ways to do the other tasks you mention.

jwe