Module gdiis 

GDIIS (Geometry Direct Inversion in Iterative Subspace) implementation GDIIS (Geometry Direct Inversion in Iterative Subspace) implementation.

This module implements the experimental GDIIS algorithm

Algorithm Overview

GDIIS accelerates geometry optimization by constructing an optimal linear combination of previous geometries and error vectors. The method:

1. Builds an overlap matrix A from error vectors: A[i,j] = <e_i, e_j>
2. Maintains A⁻¹ using SR1 (Symmetric Rank-One) updates
3. Solves for coefficients c such that Σc_i = 1 and residual is minimized
4. Validates solution using cosine and coefficient checks

Structs

DiisCoeffSolver

DIIS coefficient solver using SR1 inverse updates.

GdiisOptimizer

Main GDIIS optimizer.

TriangularMatrix

Lower triangular matrix storage for DIIS overlap matrix.

Enums

CoeffCheckMode

Coefficient check mode for GDIIS validation.

CosineCheckMode

Cosine check mode for GDIIS validation.

GdiisError

Error types for GDIIS operations.

Functions

variable_cos_limit

Returns variable cosine limit based on number of vectors used.