On 4.1.2011 11:15, Ulrich Eckhardt wrote:
Zdenko wrote:
Please, can anybody write me a simple recursive matrix multiplication
using multiple threads in Python, or at least show me some guidelines
how to write it myself
No problem, I just need your bank account data to withdraw the payment and
the address of your teacher whom to send the results. ;^)
Seriously, things don't work like this. If you show effort, you will get
help, but you don't get working solutions without even a bit of effort on
your own.
Start with a recursive algorithm, then make it multithreaded. Be prepared to
make some experiments on how to distribute tasks to threads and collect
them again.
Uli
Ok, I expected something like this :)
Lets try this way:
I wrote these two codes for example:
this one is naive way of matrix multiplication using one thread
from random import *
from time import clock
import threading
t0 = clock()
A=[]
B=[]
C=[]
m=300 #size of matrix m x m
for i in range(m):
A.append([])
B.append([])
C.append([])
for j in range(m):
A[i].append(randint(1,9))
B[i].append(randint(1,9))
C[i].append(0)
class MyThread ( threading.Thread ):
def run ( self ):
for i in range(m):
for j in range(m):
for k in range(m):
C[i][j]+=A[i][k]*B[k][j]
t=MyThread()
t.start()
t.join()
print clock() - t0, "seconds"
this one is using two threads, each one is multiplying half of matrix
import time
from threading import Thread
from random import randint
t0 = time.clock()
class MyThread(Thread):
def __init__(self, poc, kr):
Thread.__init__(self)
self.poc=poc
self.kr=kr
def run(self):
for i in range(self.poc,self.kr):
for j in range(m):
for k in range(m):
C[i][j]+=A[i][k]*B[k][j]
A=[]
B=[]
C=[]
m=300 #size of matrix m x m
for i in range(m):
A.append([])
B.append([])
C.append([])
for j in range(m):
A[i].append(randint(1,9))
B[i].append(randint(1,9))
C[i].append(0)
thr1=MyThread(0,m/2)
thr2=MyThread(m/2,m)
thr1.start()
thr2.start()
thr1.join()
thr2.join()
print time.clock() - t0, "seconds"
why is second one more than twice slower than first when it should be
faster. I suspect that problem is in simultaneous access to matrix C but
i don't know how to solve this.
I used this just for example to see how the threading works so i can
work on recursive and Strassen algorithm.
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