(HP71B) Eigenvalues of Symmetric Real Matrix

[Albert Chan]

Hi, Werner

Sorry for the confusion.
I am basing on bij = tan( 1/4 * (2θ = atan(2*aij / (aii - ajj))) )      , i ≠ j, aij ≠ 0

Except edge cases, bij = tan(θ/2)      , |θ/2| ≤ pi/8 ≈ 0.3927

From https://en.wikipedia.org/wiki/Cayley_transform#Examples, this may be why AFH code work.



LHS matches AFH code of half-angle tan, reversed sign, and zero diagonal.
RHS = Cayley transformed LHS, matches rotation matrix.

Perhaps same idea can be extended from 2x2 to nxn matrix?