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 ▼ Antonio Maschio (Italy) Senior Member Posts: 416 Threads: 78 Joined: Mar 2006 04-21-2006, 11:22 AM I cannot find in the manual the following answer: what does this matrix descriptor mean? ```C-- 2 2 ``` I know that C means matrix C, and 2 2 are the rows/columns. but why the two dashes? What do they mean? -- Antonio ▼ Valentin Albillo Posting Freak Posts: 1,755 Threads: 112 Joined: Jan 2005 04-21-2006, 11:53 AM The matrix has been subjected to system solving or determinant calculation and as a result it is now an LU decomposition, signified by two dashes. Have a look at the top of pages 148 and 160 of the HP-15C's Owner's Manual. Best regards from V. Edited: 21 Apr 2006, 11:55 a.m. ▼ Antonio Maschio (Italy) Senior Member Posts: 416 Threads: 78 Joined: Mar 2006 04-21-2006, 12:00 PM Ok, thanks, I didn't find it. -- Antonio Karl Schneider Posting Freak Posts: 1,792 Threads: 62 Joined: Jan 2005 04-21-2006, 03:39 PM Antonio -- Valentin is, of course, correct. The "--" indicates that the matrix has been replaced by an encoded form of an LU decomposition, which takes no more space than the original matrix. Linear-system solutions are often computed much more quickly using the LU decomposition of the original matrix. This is useful when computing multiple linear-system solutions using the same system matrix. The determinant of an LU matrix is trivially simple to compute. When solving a system of equations, the original matrix is replaced by the encoded LU decomposition. However, when calculating the determinant of a matrix, the encoded LU decomposition is stored to the RESULT matrix. This will increase the amount of matrix storage space required, unless the identifier of the RESULT matrix is the same as that of the original matrix. Users should keep this in mind if an attempt to calculate the determinant produces a puzzling "Error 10" message (not enough free memory). More-detailed information about the LU decomposition as implemented in the HP-15C can be found in Section 4 of the HP-15C Advanced Functions Handbook. A scan of this manual is available on the MoHPC CD- and DVD-ROM sets. Regards, -- KS Edited: 25 Apr 2006, 3:14 a.m.

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