Torture tests: what do they mean?

[DavidM]

(05-15-2014 06:01 PM)jebem Wrote:  Test 1:
(sqrt(6)^2)-6
So, the expected precise result should be Zero, right?

I have a 50g, but not the Prime. So my comments are limited to that platform.

I've highlighted what I believe to be a key phrase in your above test. You are expecting a precise result, but you're apparently using the calculator in the mode which (by design) gives approximate results. If you change your calculator to "Exact Mode On" (system flag 105 cleared) I believe you'll find a more acceptable result. Exact/Approximate mode can be toggled by holding down the right arrow key (without releasing), then pressing and releasing the Enter key.

(05-15-2014 06:01 PM)jebem Wrote:  Test 2:
(10^15 + 7.2 − 10^15) * 100
The expected result should be 720.

This one's similar to the above, but there's a subtlety that needs to be pointed out.

First, make sure you're in Exact/CAS mode.

Here's the tricky part: The inclusion of "7.2" in that expression acts as a signal to the expression parser that approximate values are included. This causes the entire expression to then be evaluated in Approximate mode, which in turn causes the limitation to 12 digits of precision for the whole expression. If you replace 7.2 with "72/10", I think you'll see that the results are different.

In this particular case, knowing how your various calculators operate can make a big difference in the outcome. I'm not trying to suggest that what they are doing is right/wrong/good/bad. At this point in time, it's reasonable to assume that technology has improved enough to give us more intelligent tools. But keep in mind, the technology of the 50g is now quite dated by today's standards. I believe the Prime inherited much of the same benefits/issues for floating point operations as the 50g (when not in CAS mode). Increasing the precision for non-symbolic operations would require a major architectural change for the Prime. It's certainly not impossible, but I wouldn't expect to see something like that any time soon (if ever).

So I guess I'm saying: I understand your frustration, but a little better understanding of how the tools are currently designed to work might give you a more acceptable (and predictable) experience. And there's nothing wrong with expecting more from the tools themselves. As consumers, we should always do that.