Pathologically Eclectic Rubbish Lister PerlMonks

### Re^2: Sparse Matrix Multiplication Problem

by neversaint (Deacon)
 on Jan 30, 2009 at 09:07 UTC ( #740124=note: print w/replies, xml ) Need Help??

in reply to Re: Sparse Matrix Multiplication Problem
in thread Sparse Matrix Multiplication Problem

Dear oshalla,
Thank you so much for your reply. It is truly useful.

I also tried to modify your code to do multiplication of transpose of the sparse matrix. With the following code:
```use Data::Dumper;
my @realval = (
0.994704478,
0.989459074,
0.994717023,
1.000000000,
1.000000000,
0.002647761,
0.005282977,
0.000882587,
0.005270463,
0.000882587,
0.002635231,
0.000882587,
0.002635231,);

my @row_index = qw( 1 2 3 4 5 1 3 1 2 1 2 1 2);
my @col_index =  qw(1 2 3 4 5 5 3 2 1 3 3 4 4);
my @mat_dim  = (5,5); # M always equal to N

my @trans_r = (0) x scalar(@p);

for my \$j (0..\$#row_index) {
\$trans_r[\$col_index[\$i]-1] += \$realval[\$i] * \$p[\$row_index[\$i]-1] ;
}

print Dumper \@trans_r;
[download]```
Not sure why it doesn't give this desired result:
```@result = (0.3989359, 0.1982448, 0.2008801, 0.2008801, 0.2010591);
[download]```
Truly need your expert advice on this. Thanks and hope to hear from you again.

---
neversaint and everlastingly indebted.......

Replies are listed 'Best First'.
Re^3: Sparse Matrix Multiplication Problem
by gone2015 (Deacon) on Jan 30, 2009 at 09:50 UTC

You really should make friends with use strict and its cousin use warnings... With the code as given:

• use strict complains about \$i, which is used in the loop, but doesn't seem to be declared anywhere

-- that's what it means by 'Global symbol "\$i" requires explicit package name'... we just have to accept that when looked at from the correct angle, this makes perfect sense.

• use warnings would warn you that each time \$i is used it is uninitialised (though with use strict you wouldn't get that far !).</c>

Log In?
 Username: Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://740124]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others imbibing at the Monastery: (3)
As of 2020-02-24 00:46 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?
What numbers are you going to focus on primarily in 2020?

Results (104 votes). Check out past polls.

Notices?