Hello,
I have found unexpected, astonishing results using the PDL matrix inv()
function by 2 different ways.
In the first way I manipulate PDL objects all the way, in the second way
I recreate objects by pasting values of the original PDL object into a
new PDL object.
First way gives unexpected, wrong result, second way leads to accurate
result. I do not understand this and it worries me a bit as I am
supposed to use intensively PDL matrix functions.
Anybody can give me an explanation of this, and tell me what I should do
differently when I manipulate objects?
Here is what I did :
# step 1A : creating a (2,2) matrix
Perl> my $m = random(2,2)
$PDL1 =
[
[0.65707276 0.12124598]
[0.95303134 0.43850649]
]
;
# step 1B : computing cov table of the matrix
Perl> my $c = $m->cov_table()
$PDL1 =
[
[0.071777584 0.068924048]
[0.068924048 0.066183954]
]
;
# step 1C : testing if the the matrix multiplied by its inverse is equal
to identity matrix
Perl> $c x inv($c)
$PDL1 =
[
[ 1 0]
[-0.125 1.125]
]
;
# we observe that step 1C leads to unexpected result
# step 2A : pasting the content of PDL obtained in step 1B to a new PDL
object : the 2 PDL objects are supposedly perfectly identical
Perl> $m = pdl([0.071777584,0.068924048],[0.068924048,0.066183954])
$PDL1 =
[
[0.071777584 0.068924048]
[0.068924048 0.066183954]
]
;
# step 2B : same as step 1C, testing if the the matrix multiplied by its
inverse is equal to identity matrix
Perl> $m x $m->inv()
$PDL1 =
[
[1 0]
[0 1]
]
;
# we observe that step 2B leads to expected result
Thank you.
Best regards.
Stéphane
_______________________________________________
Perldl mailing list
[email protected]
http://mailman.jach.hawaii.edu/mailman/listinfo/perldl
