Function gediis_blend_step 

pub fn gediis_blend_step(opt_state: &OptimizationState_blend) -> DVector<f64>

GEDIIS_blend step: pure interpolation using Taylor expansion B-matrix.

Algorithm

1. Build combined forces: F_i = g_vec_i + f_vec_i
2. Build Taylor E-matrix: E[i,j] = -(F_i-F_j).(X_i-X_j)
3. Build block matrix: [[E, 1], [1^T, 0]]
4. RHS: [-E_hist[0], ..., -E_hist[n-1], 1]^T
5. Solve for coefficients, drop last
6. Interpolate geometry and force

Key Difference from gdiis_blend_step

• NO Newton correction — pure interpolation only
• B-matrix uses Taylor energy overlaps, not GDIIS error vectors
• RHS incorporates energy values
• NO step control (step control is applied AFTER the blend in the hybrid)

Arguments

• opt_state - Optimization state with geometry, force, and energy history.

Returns

The purely interpolated geometry (X_interp_ediis).