Thanks for the workaround. I've reported the bug here:
https://issues.apache.org/jira/browse/MATH-691
Regards,
Warren Tang <http://blog.tangcs.com>
On Sunday, October 16, 2011 11:24:26 PM, Mikkel Meyer Andersen wrote:
Dear Warren,
This is probably a bug. Sorry for this. Would you be so kind to report
it as described on http://commons.apache.org/math/issue-tracking.html
.
What you can do instead is this:
int[] scores = {1, 2, 3, 4};
SummaryStatistics stats = new SummaryStatistics();
for(int i : scores) {
stats.addValue(i);
}
double sd = FastMath.sqrt(stats.getSecondMoment() / stats.getN());
System.out.println(sd);
So, calculating sd as:
double sd = FastMath.sqrt(stats.getSecondMoment() / stats.getN());
And then there is no need to stats.setVarianceImpl(new Variance(false)).
Cheers, Mikkel.
2011/10/16 Warren Tang <[email protected]>:
Hi, Mikkel
I'm using commons-math 2.2. The code to reproduce the issue.
import org.apache.commons.math.stat.descriptive.SummaryStatistics;
import org.apache.commons.math.stat.descriptive.moment.Variance;
@Test public void testStandardDeviation() {
int[] scores = {1, 2, 3, 4};
SummaryStatistics stats = new SummaryStatistics();
stats.setVarianceImpl(new Variance(false)); //use "population variance"
for(int i : scores) {
stats.addValue(i);
}
double sd = stats.getStandardDeviation();
System.out.println(sd);
}
Regards,
Warren Tang <http://blog.tangcs.com>
On 10/16/2011 10:43 PM, Mikkel Meyer Andersen wrote:
Dear Warren,
Could you provide values for the scores-variable in the current
example making it possible to reproduce?
Are you in fact using version 1.2 as reflected by the link you gave?
Or which version are you using?
Cheers, Mikkel.
2011/10/16 Warren Tang<[email protected]>:
Hello, everyone
I'm trying to get a "population standard deviation
<http://commons.apache.org/math/api-1.2/org/apache/commons/math/stat/descriptive/moment/StandardDeviation.html>"
(non-bias-corrected) from SummaryStatistics.
This is what I did:
SummaryStatistics stats = new SummaryStatistics();
stats.setVarianceImpl(new Variance(false)); //use "population variance"
( sum((x_i - mean)^2) / n )
for(int i : scores) {
stats.addValue(i);
}
double sd = stats.getStandardDeviation();
However, the value of "sd" is "NaN". How can I do it correctly?
--
Regards,
Warren Tang<http://blog.tangcs.com>
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
