HP Forum Archive 18

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Function arc length on 50G Message #1 Posted by Hal Bitton in Boise on 25 Aug 2008, 10:06 a.m. Hi folks, Is there an indigenous function on the 50G that will let me find the arc length along a given function line between two limits? I can't seem to find reference to such functionality in the users guide. Thanks and best regards, Hal

Re: Function arc length on 50G Message #2 Posted by George Bailey (Bedford Falls) on 25 Aug 2008, 10:54 a.m., in response to message #1 by Hal Bitton in Boise >>>CLICK<<< I don't think there is a dedicated function available. But with the formula from the above article, you might want to write a tiny program of your own... (I suspect you know that formula already) Edited: 25 Aug 2008, 12:42 p.m.

Re: Function arc length on 50G Message #3 Posted by Hal Bitton in Boise on 25 Aug 2008, 5:15 p.m., in response to message #2 by George Bailey (Bedford Falls) Thanks George, I had actually already written a program for my 42S that solves for arc length iteratively/numerically (where I can specify the number of iterations), which of course is pretty straightfoward, and will work on any function. I was just wondering if this was pre-programed on the 50G (like it is on the TI89). Guess I'll have to write an RPL subroutine for my 50G to solve for arc length (uhggg...RPL is not easy for me!). Thanks and best regards, Hal

Re: Function arc length on 50G Message #4 Posted by Marcus von Cube, Germany on 26 Aug 2008, 3:49 a.m., in response to message #2 by George Bailey (Bedford Falls) The 50g makes it easy to define the function yourself: 'AL(a,b,f,x)=Integral(a,b,SQRT(1+SQ(DERIV(f,x))),x)' DEF Substitute the words in italics by their respective symbols. This defines the variable AL as a short program with just an arithmetic expression (the right hand side of the above equation) as its body. The function takes parameters similar to the built in symbolic integration. You'll have to force numeric evaluation (->NUM) if you want to see numeric results. If anybody detects a typo, please correct me.

Re: Function arc length on 50G Message #5 Posted by George Bailey (Bedford Falls) on 26 Aug 2008, 4:17 a.m., in response to message #4 by Marcus von Cube, Germany Marcus, thanks, it works great, no typo! Just don't forget to purge x before executing AL, in case you have stored a value in it..: ;-) Or else you'll get an error!

Re: Function arc length on 50G Message #6 Posted by Marcus von Cube, Germany on 26 Aug 2008, 6:27 a.m., in response to message #5 by George Bailey (Bedford Falls) If you use lower case variable names the danger of having accidently stored anything there is low. The program creates four local variables: a, b, f and x. I was hoping that x in the expression is treated as a local formal variable. I'm not sure if that works. If the local variable x holds the name of the variable passed as the 4th argument to AL, this name matters. If you pass X and X exists and holds a value you might get into trouble.

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