Vectorization

[Paul McGuire]

"RonnyM" <ronnyma at math.uio.no> wrote in message
news:1149595753.611358.189070 at i39g2000cwa.googlegroups.com...
> Hi!
>
> Need to vectorize this, but do not have a clue.
>
> a = n*m matrix
> x and y are n and m vectors
>
> Suggestions?
>
>
>
> def fill(a, x, y):
>     for i in range(1,a.shape[0]):
>         xp = x[i]
>         for j in range(a.shape[1]):
>             yp = y[j]
>             a[i,j] = sin(xp*yp)*exp(-xp*yp) + a[i-1,j]
>     return a
>
> Thanks in advance,
>
> Ronny Mandal
>

Something like this, but the first row in a is never modified, is this
correct?

Note: this is a brute force Python attempt at a matrix, using a list of
lists.  Look also at the array and numarray modules.

-- Paul


from math import sin,exp

def fill(a,x,y):
    aRowCount = len(x)
    aColCount = len(y)
    #a = [[0]*aColCount for i in range(aRowCount)]
    for ii,xp in enumerate(x[1:]):
        i = ii+1
        for j,yp in enumerate(y):
            a[i][j] = sin(xp*yp)*exp(-xp*yp) + a[i-1][j]
    return a

or more tersely (note - no side-effect of modifying a in place, makes a new
copy):

def fill2(a,x,y):
    fn = lambda t,u,v:sin(t*u)*exp(-t*u) + v
    return [a[0]] + [ [ fn(xp,yp,aa) for (yp,aa) in zip(y,arow) ] for
(xp,arow) in zip(x[1:],a[:-1]) ]