|Re: [WP 34S] Expanded and rearranged manual available|
Message #5 Posted by Dieter on 18 Aug 2012, 5:12 p.m.,
in response to message #1 by Walter B
I don't know whether this is a problem of the manual or the current implementation, and the way SLV works has been discussed recently, but anyway:
SLV seems to work better than in previous versions. For instance it no longer throws an error if the best possible function result exceeds 1E-16. However, either the implementation or the manual is wrong: the latter states that the user provides two guesses and "for the rest, the user interface is as in the HP-15C". It's not. And since the algorithms in the 15C and 34s are completely different, also the results differ. So this reference is misleading.
Example (tested on 3.1 3225):
1 [ENTER] 2 [SLV] 99 => X=1,4142 Y = 1,4166 Z = 1,4142 (= X)
Do the same on a 15C (or 34C) and X and Y will contain the two best possible solutions 1,414213562 resp. ...63 while Z holds f(X) = -1E-9.
Or try the previous example with initial guesses 2 and 3. This will throw a +infinity error on the 34s, while the classis HPs return the correct result.
So the 34s obviously does not return the same results, and unlike the 15C/34C it also does not return f(X) in Z (which in this case would be approx. -9E-11). The accuracy of the result depends from the display setting, i.e. FIX 4 and ALL will return different results. These are only as exact as the display setting, while the 34C/15C always return the best possible root(s). This behaviour should get documented and the 15C reference should be omitted.
Please don't get me wrong: SLV works well, but it is completely different from the 15C/34C. And yes, I would like to get results that are independent from the display setting. But the essential point is that the manual and the way the 34s works simply do not agree.