Hi
the constructor is the same also in the second case. I run two times
the same code, one using mean = 1 and in the second mean = -1.
Ok, I need to understand what a JIRA is then I'll attach a unit test ;-)
I have the last question:
I need to compute the covariance matrix of some input data to compute
the Mahalanobis distance. In my data, the number of features is
bigger than the number of docs, and these data are very sparse. I
cannot compute the covariance matrix using the classic approach,
because it becomes very time and computational expensive. Is there any
implementation of an approximate way to compute it in Mahout? I have
had a look in the library, but I do not find it.
thanks for your help
Marco
On 20 Jul 2011, at 19:15, Ted Dunning wrote:
Well, that is hard to understand without a complete test case. In
the first
case you have a vector with one element constructed while in the
second
case, you wind up with two elements and don't show the constructor.
Write up a JIRA and attach a unit test.
My strong expectation is that this is a case of refrigerator
blindness.
On Wed, Jul 20, 2011 at 9:22 AM, Marco Turchi
<[email protected]>wrote:
Hi
you are right about the sparse vector issue... but I'm constructing
distV
in the same way changing only + and - in the variable mean. In both
the
cases, I should have the same number of entries in the final vector.
Thanks a lot for your help
Marco
On 20 Jul 2011, at 17:42, Ted Dunning wrote:
You constructed the first vector with a dimension of 1. It looks
like you
constructed the second one with a larger dimension of 2.
When you offset a sparse vector, all of the zeros become non-zero
and the
vector becomes dense. This results in a bunch of cells being
created.
On Wed, Jul 20, 2011 at 6:28 AM, marco turchi
<[email protected]
wrote:
Dear All,
I have a strange behaviour when I use the method Plus for Vector.
I have a RandomAccessSparseVector vector, if I add a positive
number, I
got
a new Vector where each element is the sum of the old value plus
the
positive number. While if I add a negative number, the new vector
has 1
more
entry:
RandomAccessSparseVector distV = new RandomAccessSparseVector(1);
distV.setQuick(0,1);
double mean = 1;
RandomAccessSparseVector app =
(RandomAccessSparseVector)(**distV.plus(mean));
the output is
{0:2.0}
if I have
double mean = -1;
RandomAccessSparseVector app =
(RandomAccessSparseVector)(**distV.plus(mean));
the output is
{1:1.0,0:-1.0}
For sure I'm doing something wrong. Do you have any ideas where the
problem
is?
Thanks a lot in advance
Marco
