3x3 matrix operations for the HP12C Part II Message #1 Posted by Kalevipoeg on 9 Aug 2007, 3:25 a.m.
I posted the Cramer’s rule for the HP12c on February 2005.
http://www.hpmuseum.org/cgisys/cgiwrap/hpmuseum/archv014.cgi?read=68690
Now I have played with matrices and the HP12C again.
My old 12C can find the inverse of the 3x3 matrix and pretty quickly too.
Here is my procedure. You may wonder that there is no GTO command in this program. Yes, that´s true. It wasn´t necessary.
01 RCL 5 21 RCL 8 41 RCL 8 61 /
02 RCL 9 22 * 42 * 62 R/S
03 * 23 RCL 5 43  63 RCL 5
04 RCL 6 24 RCL 7 43 RCL 0 64 RCL 8
05 RCL 8 25 * 45 / 65 RCL 2
06 * 26  46 R/S 66 STO 8
07  27 RCL 3 47 RCL 4 67 RDN
08 RCL 1 28 * 48 RCL 7 68 STO 5
09 * 29 + 49 RCL 1 69 RCL 1
10 RCL 6 30 STO 0 50 STO 7 70 *
11 RCL 7 31 RCL 6 51 RDN 71 X<>Y
12 * 32 RCL 9 52 STO 4 72 STO 2
13 RCL 4 33 RCL 3 53 RCL 3 73 RCL 4
14 RCL 9 34 STO 9 54 * 74 *
15 * 35 RDN 55 X<>Y 75 
16  36 STO 6 56 STO 1 76 RCL 0
17 RCL 2 37 RCL 5 57 RCL 6 77 /
18 * 38 * 58 *
19 + 39 X<>Y 59 
20 RCL 4 40 STO 3 60 RCL 0
User instructions:
Store elements of matrix A in row order into registers R_{1} through R_{9}. C=A^{1}. Press R/S to calculate c_{11}. Press R/S to calculate c_{21}. Press R/S to calculate c_{31}. Press R/S to calculate c_{12}. Press R/S to calculate c_{22} etc.
You can press RCL 0 to find the determinant of A.
