Re: [Numpy-discussion] matrix multipln takes too much time

Dec. 25, 2007


      you can either use matrix multiplication (see resultmatrix2) or tensordot
(see resultmatrix3).
on my computer I have:
1.    15.6 sec with your code
2.    0.072 sec with resultmatrix2
3.    0.040 sec with tensordot (resultmatrix3) (-- which is a 400x speed)

--------------------------------------------

from numpy import *

items=25
sample=5
totalcols=8100
#matrixone=matrix(zeros((items,totalcols)))
#matrixtwo=matrix(zeros((items,totalcols)))

matrixone=matrix(random.rand(items, totalcols))
matrixtwo=matrix(random.rand(items, totalcols))

resultmatrix=matrix(zeros((items,sample)))
resultmatrix2=matrix(zeros((items,sample)))
resultmatrix3=matrix(zeros((items,sample)))

# your code
for i in range(items):
    for j in range(sample):
        tval=0.0
        for p in range(totalcols):
            tval +=matrixone[ j , p ] * matrixtwo[ i , p ]
        resultmatrix[ i, j ]=abs(tval)

# matrix multiplication
for i in range(items):
    for j in range(sample):
        resultmatrix2[ i, j ] = abs(matrixone[j,:] * matrixtwo[i,:].T)

# tensordot
resulmatrix3 = tensordot(matrixone[:sample,:], matrixtwo.T, axes=1).T

---------------------------------------

hth,
L.


On Dec 25, 2007 5:16 PM, Louis Wicker <Louis.Wicker@noaa.gov> wrote:
...
Hi there - quick suggestion on Xmas morning - others are much more
familar.
You do not want to use a loop to do the matrix multiply, you want to use
the intrinsic functions assoicated with matrix.
So you want something like
res = Math.abs( matmul(arrayone, arraytwo) )
note - that is not real code, just symbolic code.  I am sure this is
easily found in the documentation.
cheers!
Lou
On Dec 25, 2007, at 8:47 AM, devnew@gmail.c om <devnew@gmail.com> w
le-interchange-newline">
hi
i am doing some maths calculations involving matrices of double values
using numpy.matrix ,
java code for this is something like
int items=25;
int sample=5;
int totalcols=8100;
double[][]dblarrayone=new double[items][totalcols];
double[][]dblarraytwo=new double[items][totalcols];
//their elements are set elsewhere before calculation
double[][] resultarray = new double[items][sample];
for(int i=0;i<items;i++){
   for(int j=0;j<sample;j++){
       double tval=0.0;
       for(int p=0;p<totalcols;p++)
           tval+=dblarrayone[j][p] * dblarraytwo[i][p];
       resultarray[i][j]=Math.abs(tval);
}
}
so I wanted to do the same  in python ..(may b
recommended way..)
i am storing the filled matrices and other values as instance variable
of a class and access them by self.whatever...
self.items=25
self.sample=5
self.totalcols=8100
#self.matrixone,self.matrixtwo are numply matix objects with already
filled elements
#but for testing i filled it with zeros
self.matrixone=matrix(zeros((items,totalcols)))
self.matrixtwo=matrix(zeros((items,totalcols)))
resultmatrix=matrix(zeros((self.items,self.sample)))
for i in range(self.items):
   for j in range(self.sample):
        tval=0.0
        for p in range(self.totalcols):
           tval +=self.matrixone[ j , p ] * self.matrixtwo[ i , p ]
        resultmatrix[ i, j ]=abs(tval)
here I found that while the java code takes ba br>execute the code ,the
python code takes something like 53 secs to execute !!..I am baffled
by this ..can anyone advise me how i can improve this? (i want to code
in python so  I can't use c,c++ , java)
dn
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Re: [Numpy-discussion] matrix multipln takes too much time

lorenzo bolla