Bug: HP Prime can't do Log's

[cyrille de brébisson]

Hello,

Precision is, as always, touchy when one talks about floating points.
The classical example of 1/3*3 comes to mind (should return 0.999999... on all numerical calcs that do not try to doctor the results or mic numerical and symbolic. Hence, could claim that no calc can do math)...

Prime does give the correct answer to LN(81) and to LN(3) (within the calculator 12 digit accuracy). And dividing these 2 answers by each others do indeed yield 3.99...99).
What is 'funny' is that removing 2 digits of accuracy to these results and doing the division, will yield (after rounding), 4. A 'more precise result'.

So, we are in the 'interesting case' where more precision returns a less accurate result, and less precision will return a more accurate result.

This is, as noted above, a normal occurrence of floating point arithmetic.


People do tend to forget that Floating point arithmetic is rarely exact (the cases where it is are, from a statistic standpoint, rare). But is designed to be self consistent and to avoid accumulation of errors on long calculations.


Now, of course, as stated by someone earlier, if you want 'exact' math (not precise, but exact), then you can use the CAS where logb(81,3) will return 4. You can find logb in the template menu/key (next to the x,t,theta key).

> "In the area of math, there still is a right vs. wrong answer"
This can (and often is) debated, and is a very interesting question all by itself!
Everyone would agree that, in lots of math problems, there is not 'a right answer', but 0 to n right answers to a question (some questions do not have answers, and some do have more than 1)...
I am pretty sure that they are some provably wrong answers to a given questions (ie, an answer that can not be justified)
Gödel has nicely proven that they are some undecidable answers to some questions (ie, answers for which we can not know if they are right or wrong).
Of course, there is always the problem of interpretation and context of the question/answer pair.
The same answer can be right in a given context and wrong in another (6+6=2, in the context of 10 mod arithmetic).
In the case at hand, LN(81,3)=3.999..99 in the context of 12 digit decimal precision floating point arithmetic. It is equal to 4 in the context of 10 digit precision floating point!

I guess that aspect of things is why I like math. Not for the calculation but for the "philosophy" (phylosomath) behind it!

Cyrille