Vectorization

[RonnyM]

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

[Paul McGuire]

Re: Vectorization

"RonnyM" <ronnyma@math.u io.no> wrote in message
news:1149595753 .611358.189070@ i39g2000cwa.goo glegroups.com.. .[color=blue]
> 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
>[/color]

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]) ]

[Robert Kern]

Re: Vectorization

Paul McGuire wrote:[color=blue]
> "RonnyM" <ronnyma@math.u io.no> wrote in message
> news:1149595753 .611358.189070@ i39g2000cwa.goo glegroups.com.. .
>[color=green]
>>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[/color]
>
> 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.[/color]

The array module doesn't do matrices, and numarray is deprecated. Please point
new users to numpy, instead.

http://numeric.scipy.org/

Since the OP seems to already be using one of Numeric/numarray/numpy, (given
"a.shape"), I would suggest that he ask the question on the appropriate mailing
list:

https://lists.sourceforge.net/lists/listinfo/numpy-discussion

I won't attempt an answer until the OP answers about the first row.

--
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