Function update_hessian_advanced 

pub fn update_hessian_advanced(
    hessian: &DMatrix<f64>,
    delta_x: &DVector<f64>,
    delta_g: &DVector<f64>,
    method: HessianUpdateMethod,
) -> DMatrix<f64>

Updates the Hessian matrix using the specified method from the hessian_update module.

This function provides access to multiple Hessian update algorithms ported from the Gaussian Fortran source code (D2CorX subroutine).

Available Methods

• Bfgs: Standard BFGS for minima (with curvature check)
• Bofill: Weighted Powell/Murtagh-Sargent for saddle points
• Powell: Symmetric rank-one update
• BfgsPure: BFGS without curvature check
• BfgsPowellMix: Adaptive blend of BFGS and Powell

Arguments

• hessian - Current Hessian matrix (Ha/Ų)
• delta_x - Step vector (x_new - x_old) in A
• delta_g - Gradient difference (g_new - g_old) in Ha/A
• method - Update method to use

Returns

Updated Hessian matrix in Ha/Ų.