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HP Forum Archive 14

 solve 3x3 system on 33sMessage #1 Posted by martin cohen on 30 May 2004, 11:57 a.m. Here is some code for the 33s (originally written for the 32sii) for solving a 3x3 linear system of equations. The code uses Cramer's rule ( with determinants) and does not change the coefficients. ```Solve a 3 x 3 system of linear equations A*X + B*Y + C*Z = D E*X + F*Y + G*Z = H I*X + J*Y + K*Z = L DET = |A B C| |E F G| |I J K| = A * (F K - G J) - E * (B K - C J) + I * (B G - C F) D_X = |D B C| |H F G| |L J K| Same for D_Y and D_Z x = D_X/DET,, ... =============================================================================== S: do via determinants and column swapping (20 steps, 43.5, E8A7): LBL S XEQ U; STO W; VIEW W 1; XEQ V; XEQ U; RCL/ W; STO X; 1; XEQ V 2; XEQ V; XEQ U; RCL/ W; STO Y; 2; XEQ V 3; XEQ V; XEQ U; RCL/ W; STO Z; 3; XEQ V RTN U: determinant of [ [a, b, c], [e, f, g], [i, j, k] ] (33.0, A5DB) LBL U // DET = A * (F K - G J) - E * (B K - C J) + I * (B G - C F) RCL F; RCL* K; RCL G; RCL* J; -; RCL* A; RCL B; RCL* K; RCL C; RCL* J; -; RCL* E; - RCL B; RCL* G; RCL C; RCL* F; -; RCL* I; + RTN V: swap column in x reg (1..3) with [d, h, l] (24.0, 8BD5) LBL V STO i; RCL D; X<> (i); STO D; 4; STO+ i; RCL H; X<> (i); STO H; 4; STO+ i; RCL L; X<> (i); STO L; RTN I: input a 3x3 system (also uses lbl J) lbl I 1.012 STO I LBL J INPUT (I) ISG I GTO J RTN ```

 Re: solve 3x3 system on 33sMessage #2 Posted by Eddie Shore on 1 June 2004, 9:53 a.m.,in response to message #1 by martin cohen Nice work, Martin.

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