Re: Even More Simultaneous Equation Solutions « Next Oldest | Next Newest »

 ▼ JasonG Junior Member Posts: 25 Threads: 8 Joined: Jan 1970 03-31-2006, 08:42 AM Hi all, Okay then, I may have been somewhat "previous" in selling my 49G+ last year and replacing it with a TI84+SE as I have been having problems with the TI which are closely related to the problem discussed here. In short, Valentin's A-matrix cannot be effectively inverted in the TI as the lack of precision leads to the conclusion that the matrix is singular. :-( I'll admit it here, I made a mistake! I will be sorting out monies for a new 49G+ shortly to tide me over until the OpenRPN project comes to fruition. Tra JasonG ▼ Palmer O. Hanson, Jr. Posting Freak Posts: 901 Threads: 113 Joined: Jun 2007 03-31-2006, 10:17 PM Jason: The TI-83 Plus calculates the determinant of Valentin's matrix A to be zero which prevents doing an INV A * B solution on that machine. The TI-85 calculates the determinant of Valentin's matrix A to be 9.90927530944e-08 which is within one per cent of the exact value of 1e-07. As indicated in the first submission in this thread the TI-85 gets respectable solutions for Valentin's problem whether using the INV A * B or Simultaneous Equation method. What does the TI-84 find as the determinant of A? In a thread in 2005 I presented results from calculation of determinants for 7x7 through 10x10 Hilbert matrices as follows: ``` 7x7 8x8 9x9 10x10 TI-83+ 4.835795E-25 2.737004E-33 9.721266E-43 0 TI-85 4.835795E-25 2.737004E-33 9.721266E-43 2.207089E-53 HP-49 Exact 4.835803E-25 2.737050E-33 9.720234E-43 2.164179E-53 ``` where the surprise was that the TI-83 Plus and TI-85 determinants for 7x7 through 9x9 were exactly the same and quite respectable but the TI-83 Plus determinant for the 10x10 Hilbert was zero. What does the TI-84 yield for those calculations? ▼ JaSon Junior Member Posts: 42 Threads: 23 Joined: Aug 2007 04-04-2006, 04:38 AM Well, my TI84+SE gives the determinant of A (where A is from the original system at the top of this thread) as zero. Not nearly zero but precisely zero. :-( It's a shame really as I quite like the TI84 in many ways, it's not a bad calculator. I suppose I'll have to dig out my 85 (if I can find it) and give that a go as I'm still unsure about the quality issues with the 49G+. ttfn Jason ▼ Palmer O. Hanson, Jr. Posting Freak Posts: 901 Threads: 113 Joined: Jun 2007 04-04-2006, 10:43 PM When I told TI-CARES about the zero for the determinant of the 10x10 Hilbert they responded with some words about the TI-83+ and TI-84 being less accurate machines and suggested that I should use the TI-86 or TI-89 for that kind of problem. That's not possible in my budget right now. The TI-83+ doesn't get zero for the determinant of all 10x10 matrices. You might want to try Valentin's problem using RREF on the TI-84. On the TI-83+ and TI-85 I get ```1.53301985311 0.999932803352 1.47525070084 1.47796598162 1.00032979830 0.522041369573 0 ``` where the zero for the seventh element of the solution is truly curious. RREF on both machines solves some other seventh order systems satisfactorily. ▼ JasonG Junior Member Posts: 25 Threads: 8 Joined: Jan 1970 04-05-2006, 04:42 AM Yeah, I had spotted that. I guess it's because Valentin's problem is itself ill-conditioned, plus the method used is a little unstable (induced instability) so is bound to produce weird results. I agree that the zero is kinda odd though. :-) I will be recovering my TI85 from its current hding place at the weekend, so I should be able to have a closer look at this problem then. :-) ttfn Jason

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