Numeric CAS - Part 11: Eigenvalues of 3 x 3 Matrices

Eigenvalues of 3 x 3 Matrices

Many graphing calculators that do not have CAS (computer algebraic systems) do not have eigenvalues and eigenvector functions.

The programs for the Casio Prizm and TI-84+ gives eigenvalues of 3 x 3 matrices.

For the HP 39gii has the functions EIGENVAL for eigenvalues.

Example:
A = [[2, -2, 3][-1, 0, 1][6, -3, 3]]

Eigenvalues:
≈ 0.2465, -1.8447, 6.5982

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Casio Prizm:

EIGEN3
Eigenvalues of a 3 × 3 Matrix
Circa 2011 - 244 bytes

a+bi
"3 × 3 Matrix"? → Mat A
Mat A[1,1] + Mat A[2,2] + Mat A[3,3] → T
(Mat A)² → Mat B
Mat B[1,1] + Mat B[2,2] + Mat B[3,3] → U
Solve(-X^3 + X^2 × T + X × 1/2 × (U-T^2) + Det Mat A,0)→ R ◢
-R^2 + R × T - T^2 ÷ 2 + U ÷ 2 → A
-R + T → B
1/2 × (B - √(4A + B^2)) → E ◢
1/2 × (B + √(4A + B^2)) → F ◢
"STORED IN R, E, F"

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TI-84+:

EIGEN3
Eigenvalues of a 3 × 3 matrix - 193 bytes
12/3/12

a+bi
Input "3 X 3 MATRIX:", [A]
[A](1,1) + [A](2,2) + [A](3,3) → T
[A]² → [B]
[B](1,1) + [B](2,2) + [B](3,3) → U
solve(-X³ + X² T + .5X(U-T²) + det([A]), X, 0) → R
Pause R
-R² + RT - T²/2 + U/2 → A
-R + T → B
.5(B - √(4A+B²)) → E
.5(B + √(4A+B²)) → F
Pause E
Pause F

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This blog is property of Edward Shore. 2012