HP Forum Archive 21

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[WP 34s] Summation Function (Sigma) Message #1 Posted by Paul C on 29 Jan 2013, 2:37 a.m. Hi all, I just recently received my WP-34s and was playing around with the summation function( [g] [3] ). As searching for the solution on the manual and couldn't find an answer, I thought it would be better to post my question here. Is it possible to set a starting value and an end value for the summation function? If so, is it okay to set those value to +/-infinite while D flag is on ? cheers, Paul C.

Re: [WP 34s] Summation Function (Sigma) Message #2 Posted by Walter B on 29 Jan 2013, 2:56 a.m., in response to message #1 by Paul C Quote: Is it possible to set a starting value and an end value for the summation function? Did you look at p. 112 of the manual? Quote: If so, is it okay to set those value to +/-infinite while D flag is on ? :-) Nice idea indeed. But, alas, it isn't ok - just think of the infinite number of loops - you'd wait an infinite time for the function to finish. d:-)

Re: [WP 34s] Summation Function (Sigma) Message #3 Posted by Paul C on 29 Jan 2013, 3:21 a.m., in response to message #2 by Walter B Quote: :-) Nice idea indeed. But, alas, it isn't ok - just think of the infinite number of loops - you'd wait an infinite time for the function to finish. d:-) Oops, I should've read the manual thoroughly before posting the question :P Thanks Walter, the last sentence sounds reasonable and makes sense to me.

Re: [WP 34s] Summation Function (Sigma) Message #4 Posted by Paul Dale on 29 Jan 2013, 3:10 a.m., in response to message #1 by Paul C Quote: If so, is it okay to set those value to +/-infinite while D flag is on ? I can add support for infinite summations. Bear in mind that they count down and infinity-1 = infinity. The code would be trivial: inf? back 001 Of course it won't finish in anyones lifetime... - Pauli

Re: [WP 34s] Summation Function (Sigma) Message #5 Posted by Paul C on 29 Jan 2013, 3:26 a.m., in response to message #4 by Paul Dale Quote: I can add support for infinite summations. Bear in mind that they count down and infinity-1 = infinity. The code would be trivial: inf? back 001 Of course it won't finish in anyones lifetime... - Pauli Perhaps, an artificially high number would work in this case?

Re: [WP 34s] Summation Function (Sigma) Message #6 Posted by Walter B on 29 Jan 2013, 3:33 a.m., in response to message #5 by Paul C Quote: Perhaps, an artificially high number would work in this case? So which number do you suggest being high enough? d;-)

Re: [WP 34s] Summation Function (Sigma) Message #7 Posted by Paul Dale on 29 Jan 2013, 3:36 a.m., in response to message #6 by Walter B Quote: So which number do you suggest being high enough? Then we'll throw the summation of 1/n at it :-) - Pauli

Re: [WP 34s] Summation Function (Sigma) Message #8 Posted by Paul C on 29 Jan 2013, 3:57 a.m., in response to message #7 by Paul Dale I thought the calculator would somehow automatically notice the summation of the function (C^n) is equal to (1/1-C) if n is starting from 0 to infinite, but in this case I think the number 1000 would be high enough to replace the infinite.

Re: [WP 34s] Summation Function (Sigma) Message #9 Posted by Paul Dale on 29 Jan 2013, 4:10 a.m., in response to message #8 by Paul C The 34S does no symbolic manipulations, so it can't recognise what you want it to here. Use an RPL machine for this kind of thing, the 34S is strictly numeric. Moreover the sum from 1 to 1,000 of 1/n is 500,500 which is a very very long way from the correct answer of infinity. Thus, making summations to infinity the same as summations to 1,000 will produce incorrect answers. The 34S does not produce incorrect answers, rather it does its best to give you the correctly rounded result for what you actually ask for -- which is often not what you really want, but that is beside the point. - Pauli

Re: [WP 34s] Summation Function (Sigma) Message #10 Posted by Paul Dale on 29 Jan 2013, 3:13 p.m., in response to message #9 by Paul Dale Oops, the sum above is of n not 1/n. Oh well. Both diverge at least. - Pauli

Re: [WP 34s] Summation Function (Sigma) Message #11 Posted by Paul Dale on 29 Jan 2013, 3:35 a.m., in response to message #5 by Paul C It wouldn't work generally which means we can't accept it. Plus, the time take for millions of iterations would be huge. It would be possible to sum the series up and stop when the terms converge. I didn't write the summation to work this way and even if it did, it would make mistakes. - Pauli

Re: [WP 34s] Summation Function (Sigma) Message #12 Posted by C.Ret on 29 Jan 2013, 7:42 a.m., in response to message #5 by Paul C Quote: The code would be trivial: inf? back 001 Of course it won't finish in anyone’s lifetime... This proves that the hardware isn't powerful enough! Have you try the Duracell's power cells ? Edited: 30 Jan 2013, 3:46 a.m. after one or more responses were posted

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