The NumWorks graphing calculator [LWN.net]

The NumWorks graphing calculator

Posted Sep 30, 2017 7:08 UTC (Sat) by madhatter (subscriber, #4665)
In reply to: The NumWorks graphing calculator by jmspeex
Parent article: The NumWorks graphing calculator

For clarification, I should add that the issue is solely with the accuracy of the carried-forward Ans token, representing the answer to an earlier calculation, since that's only evaluated to 7 sig fig. The internal accuracy of the NumWorks is far higher: arcsin(arccos(arctan(tan(cos(sin(9)))))) returns 9 (in degrees mode), as it should: even my TI84+ returns 8.99999997.

That said, (sqrt(2))²-2 also returns 4.440892x10^-16, while the TI84+ returns 0.

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The NumWorks graphing calculator

Posted Oct 2, 2017 16:31 UTC (Mon) by davidstrauss (subscriber, #85867) [Link]

My point is that, for any given level of accuracy/precision, there's arithmetic you can feed it that will reveal its deficiencies. If the goal is to cleanly have the "square" and "square root" operations neutralize each other, that requires symbolic processing to be reliable. Otherwise, it's just a question of how far you can stretch the implementation before it breaks, and non-symbolic systems tend to break that way silently. Such systems yield results that are very close to the proper one but with bewildering notation (like the ones in the article).