The Museum of HP Calculators

HP Forum Archive 09

 Reducing matrix with 15CMessage #1 Posted by R Lion on 1 Dec 2002, 5:28 a.m. I'm wondering if there is a simple way for reducing a matrix with the 15c: something like REF or RREF or rref (erable) on the 48 Thanks in advance Raul

 Re: Reducing matrix with 15CMessage #2 Posted by Vieira, Luiz C. (Brazil) on 2 Dec 2002, 9:13 a.m.,in response to message #1 by R Lion Hi I've made a small research about the subject and I could not find a direct reference for both REF (Reduce to Echelon Form) and RREF (Row-Reduced Echelon Form) in the HP15C. The first reference I found is the Urroz' 'Science and Engineering Mathematics with the HP49G'. I tried some matrix manipulations in the HP15C, but no direct result for reduction. The closest related resulting object is the LU decomposition, but it is no direct reference for what you want. That's the sort of subject that amuses me: good, deep usage of HP calculators. Would you like keeping this discussion? How far have you gone? What's the primary application you have in mind? Even if it's just for studying, please, let's keep talking/writing about it. I'd like to know if you have any reference about any source/e-source for this sort of subject. Thanks.

 Re: Reducing matrix with 15CMessage #3 Posted by R Lion on 2 Dec 2002, 1:40 p.m.,in response to message #2 by Vieira, Luiz C. (Brazil) Hi Luiz: I'll try to answer your questions. If you solve a system in the 15C, you'll get a set of solution even when the system have no solution. For instance: [[1][0]]/[[1 2][1 2]] gives you the next result matrix: [[2e10][-1e10]]. I think the key for this behaviour is in page 150 of the manual:"If the matrix...does not have an inverse...the calculated inverse is the inverse of a matrix close to the original..." I don't like this... I'd prefer get an error saying clearly that the matrix does not have an inverse, so the system does not have one solution (perhaps infinite solutions, perhaps no solution). We can get this information calculating the determinant of matrix of coefficients. We'll get 1e-10 in this case, value that "is" 0. But if I'd have the reduced matrix (triangular or Gauss form) I could see if the last line has only 0's (infinite solutions) or all 0's but the last one, (no solution). Recently I have programmed the reduction in an old Casio fx 4000p: I would like to use the matrix features of the 15c for calculating without programming.I hope you understand something in this mess... Regrads. Raul

 Re: Reducing matrix with 15CMessage #4 Posted by Vieira, Luiz C. (Brazil) on 2 Dec 2002, 2:10 p.m.,in response to message #3 by R Lion Hi; I remember all of this stuff briefly, when stdying Advanced Math. I have a harcopy of the HP15C Advanced Functions Handbook and Fourth Chapter plus Appendix have a lot of good info about Matrices and Accuracy. I'm gonna find some math readings and try to get to some acceptable material ASAP. Best regards.

 Re: Reducing matrix with 15CMessage #5 Posted by R Lion on 2 Dec 2002, 2:54 p.m.,in response to message #4 by Vieira, Luiz C. (Brazil) I have the Advanced functions handbook... Nothing about this not advanced feature :-) Thanks for your time Raul

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