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*Subject*: **[OASIS Issue Tracker] Commented: (OFFICE-2632) ODF 1.2 Part 2 CD015.18.72-5.18.75 STDEV* DANGEROUS EXTRA FORMULAS**

*From*:**OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>***To*: office@lists.oasis-open.org*Date*: Tue, 13 Apr 2010 11:05:15 -0400 (EDT)

[ http://tools.oasis-open.org/issues/browse/OFFICE-2632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18397#action_18397 ] Dennis Hamilton commented on OFFICE-2632: ----------------------------------------- There are two parts to this: 1. Removal of the second formula as an additional identity in the STD* definitions. It adds nothing to the mathematical definition and it is misleading as additional valuable information. 2. With regard to approximation issues, I agree that the general statement is appropriate. However, I am talking about cases where the mathematical form is actually unstable as a method of computation, with bigger issues around approximation quality than what is shrugged off as simple rounding errors in the delivered result. With regard to (2), I am satisfied wit the new text (draft 23) in section 5.2 on this matter. > ODF 1.2 Part 2 CD01 5.18.72-5.18.75 STDEV* DANGEROUS EXTRA FORMULAS > ------------------------------------------------------------------- > > Key: OFFICE-2632 > URL: http://tools.oasis-open.org/issues/browse/OFFICE-2632 > Project: OASIS Open Document Format for Office Applications (OpenDocument) TC > Issue Type: Bug > Affects Versions: ODF 1.2 Part 2 CD 1 > Reporter: Dennis Hamilton > Fix For: ODF 1.2 Part 2 CD 2 > > > For each of the STDEV, STDEVA, STDEVP, and STDEVPA, there is an extra formula in the definitiions. > The first formula is a definition for s^2 or sigma^2 depending on whether we are talking about a sample or a set of equiprobable values. The second formula *is* mathematically equivalent but it is computationally worse. (It has the advantage that the mean does not have to be computed in advance. However, it is even worse as a computational method than the so-called "naive" mathematical definition. The second formula is equivalent to the formula 4.2.2(14) that Donald Knuth gives as an approach to be avoided because of its computational instability.) > I recommend that the second form of the formula, the one that subtracts n X xbar^2, be stricken, because it raises more questions than it answer and we have no business even suggesting it. > Furthermore, I would use the formulas to explain how the mathematical standard-deviation (or variance in the STDEVP and STDEVPA cases) is mathematically defined. I would say that the result is a computational approximation to the mathematical value, not that it returns the mathematical result. > I would then add, perhaps, > Note: Special computational methods are generally used to produce more-reliable results than achievable by direct implementation of the formula as a computational method. > A non-normative reference to the treatment in the Art of Computer Programming might be useful here (and perhaps many other places). > PS: These are also nice codefest challenges for assessing the ways that OpenFormula functions can be implemented reliably as computations from the specification and available expert materials. -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://tools.oasis-open.org/issues/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira

**References**:**[OASIS Issue Tracker] Created: (OFFICE-2632) ODF 1.2 Part 2 CD015.18.72-5.18.75 STDEV* DANGEROUS EXTRA FORMULAS***From:*OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>

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