HP50g DESOLVE Help  Printable Version + HP Forums (https://archived.hpcalc.org/museumforum) + Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum1.html) + Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum2.html) + Thread: HP50g DESOLVE Help (/thread112691.html) 
HP50g DESOLVE Help  Chuck  04242007 On page 143 of the 50G Users manual are some commands to use the DESOLVE. The second example is entering:
['d1d1y(t)+5*y(t)=2*COS(t/2)' 'y(0)=6/5' 'd1y(0)=1/2'] The solution "should" be in terms of sine and cosine, as is reported in the manual. Mine keeps the solution in terms of the complex expressions e^(a+bi), etc. I can certainly do the rewriting myself, but what possible setting am I missing to have the calculator to convert to sines and cosines? The modes I am using are: soft menues, RPN, RAD, Complex, 't' var, the usual... But I must be overlooking something. Any suggestions?
Thanks, all.
Re: HP50g DESOLVE Help  Happy HP User  04242007 Using ROM version 2.09: 1) the variable stored in 'VX' should be 't' 2) the machine should be in radians, real, exact mode: you should see RAD XYZ R = 't' at the screen top With that done, on my 50g: ['d1d1y(t)+5*y(t)=2*COS(t/2)' 'y(0)=6/5' 'd1y(0)=1/2'] 'y(t)' DESOLVE returns, and after one minor simplification: 'COS(t*1/2)*8/19+COS(t*SQRT(5))*74/75SQRT(5)/10*SIN(t*SQRT(5))' Not bad for a handheld, Maple's closed form for this ODE is quite similar.
Re: HP50g DESOLVE Help  John  04242007 Of course, flag settings are probably to blame.
One thing you could do is completely reset your 50g, or post your complete flag settings to let us see what flags are set.
Re: HP50g DESOLVE Help  Chuck  04242007 Hmmm. No go. So here's a simpler one that I tried...
['d1d1y(T)+y(T)=0' 'y(0)=2' 'd1y(0)=0'] DESOLVE returns (after a simplification)
(e^(iT))^2 + 1 It would be nice if it just gave back 2cos(T). :(
The obvious modes shown on the screen are: In the CAS MODES I have Complex checked, and Simp NonRational checked. The system flags that are checked are {27, 34, 40, 56, 57, 68, 76, 82, 90, 103, 117, 119} My version number is #2.09 Any more clues????
Thanks. Edited: 24 Apr 2007, 11:52 p.m.
Re: HP50g DESOLVE Help  Happy HP User  04252007 Change COMPLEX to REAL mode. The shortcut key method is press and hold LEFT SHIFT, then press and release the TOOL key. This is a toggle between COMPLEX to/from REAL mode. You should see the 'C' change to an 'R' and vice versa when this key sequence is done. At the top of the screen, you should see RAD XYZ DEC R='T'
Otherwise, solve your difeqs with Maple or Matlab...
Re: HP50g DESOLVE Help  Chuck  04252007 Quote: Ahhh. The Real mode makes sense now. Thanks. Normally I DO use Mathematica, or occassionally Maple, (when not not doing them on paper) but it's hard to carry my desktop computer around with me. ;) Also, I need to know what my students are capable of doing with their magic black boxes!!! Thanks again.
CHUCK Edited: 25 Apr 2007, 12:32 p.m.
Re: HP50g DESOLVE Help  Happy HP User  04252007 Your're welcome! Oh, you're students are so lucky to be able to use such marvels as an HP50!
Re: HP50g DESOLVE Help  RON ALLEN  04262007 I see you got this "Complex" problem around to a "Real" solution. My 50, even with ROM still degraded to 2.08, wants to use complex equivalents when the DE lends itself to complex solutions. (I carried a K & E "Decilon," scabbard and all, when I was a student [ University of New Orleans, 1967 and Tulane University.] I agree with you that Chuck's students have a wonderful, portable solution to quicker understanding and modeling of engineering challenges. Regards,
Ron Edited: 26 Apr 2007, 12:46 a.m.
Re: HP50g DESOLVE Help  Rich Messeder (US)  04262007 Where do you teach, Chuck? And at HS or college/university?
Rich
Re: HP50g DESOLVE Help  Chuck  04262007 Hi Rich. I'm at a twoyear college in Washington state. We're covering harmonic motion, damped, undamped, and forced, using a number of tools. Several kids have the HP50G wihich is blowing the socks off the TI's. I'm amazed at some of the things it does. When I did this in college as a student, "all" I had was the HP11C. But that was about 10years postsliderule times, so I thought I was in fat city.
