No, that’s not normal, it's not supposed to give you a runtime error. Anything that results in an answer that is Not a Number is supposed to be set to NaN, not give you a runtime error 217 and terminate. Infinity minus itself is undefined and therefore Not a Number and should be set to NaN, but I don't get NaN, I get a fatal runtime error 217. To answer your question: if you know Inf + Inf = Inf and you know Inf - Inf = Nan then Properly evaluating from left to right: Inf + Inf - Inf = Inf - Inf = NAN or if you want to do it the other way: inf - inf + inf = NaN + Inf = NaN
(+inf) + (+inf) should and does give you (+inf) (-inf) + (-inf) should and does give you (-inf) (+inf) - (+inf) should give you (NAN) but it gives you Runtime Error 217 (-inf) - (-inf) should give you (NAN) but it gives you Runtime Error 217 (+inf) + (-inf) should give you (NAN) but it gives you Runtime Error 217 (-inf) + (+inf) should give you (NAN) but it gives you Runtime Error 217 Snip from refrence at: https://en.wikipedia.org/wiki/NaN Operations generating NaN: There are three kinds of operations that can return NaN: 1. Operations with a NaN as at least one operand. 2. Indeterminate forms: a. The divisions (±0) / (±0) and (±∞) / (±∞). b. The multiplications (±0) × (±∞) and (±∞) × (±0). c. The additions (+∞) + (−∞), (−∞) + (+∞) and equivalent subtractions (+∞) − (+∞) and (−∞) − (−∞). d. The standard has alternative functions for powers: The standard pow function and the integer exponent pown function define 0⁰, 1∞, and ∞⁰ as 1. The powr function defines all three indeterminate forms as invalid operations and so returns NaN. 3. Real operations with complex results, for example: The square root of a negative number. The logarithm of a negative number. The inverse sine or cosine of a number that is less than −1 or greater than 1. #2c clearly defines that NaN is set for the above conditions that are failing with a runtime error 217 Also reference: https://www.philforhumanity.com/Infinity_Minus_Infinity.html James -----Original Message----- From: fpc-pascal [mailto:fpc-pascal-boun...@lists.freepascal.org] On Behalf Of Marco van de Voort Sent: Wednesday, June 20, 2018 9:21 AM To: FPC-Pascal users discussions <fpc-pascal@lists.freepascal.org> Subject: Re: [fpc-pascal] math with infinity and NaN In our previous episode, C Western said: > > I can do things like +infinity*2 and +infinity-3 and even > > sqr(infinity) and power(infinity,10) the results are still +Inf which is > > expected? > > ??but I can?t do anything involving subtracting infinity from > > infinity.? Isn't that normal? Otherwise, what would inf+inf-inf be if you know that (inf+inf) =inf _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
