Function square_linsolve 

pub fn square_linsolve<T, V>(
    operator: &TreeTN<T, V>,
    rhs: &TreeTN<T, V>,
    init: TreeTN<T, V>,
    center: &V,
    options: LinsolveOptions,
    input_mapping: Option<HashMap<V, IndexMapping<T::Index>>>,
    output_mapping: Option<HashMap<V, IndexMapping<T::Index>>>,
) -> Result<SquareLinsolveResult<T, V>>
where
    T: TensorLike + 'static,
    <T::Index as IndexLike>::Id: Clone + Hash + Eq + Ord + Debug + Send + Sync + 'static,
    V: Clone + Hash + Eq + Ord + Send + Sync + Debug + 'static,

Solve the linear system (a₀ + a₁ * H) |x⟩ = |b⟩ for TreeTN.

This solver is for the square case where V_in = V_out (input and output spaces are the same).

Arguments

• operator - The operator H as a TreeTN (must have compatible structure with rhs)
• rhs - The right-hand side |b⟩ as a TreeTN
• init - Initial guess for |x⟩
• center - Node to use as sweep center
• options - Solver options
• input_mapping - Optional per-node mapping from state site index to operator input index. Required when the operator (MPO) uses internal indices distinct from the state’s site indices.
• output_mapping - Optional per-node mapping from state site index to operator output index. Required when the operator (MPO) uses internal indices distinct from the state’s site indices.

Returns

The solution TreeTN, or an error if solving fails.

Example

use tensor4all_core::{DynIndex, TensorDynLen};
use tensor4all_treetn::{square_linsolve, LinsolveOptions, TreeTN};

let s = DynIndex::new_dyn(2);
let operator_tensor = TensorDynLen::from_dense(vec![s.clone()], vec![1.0, 1.0])?;
let rhs_tensor = TensorDynLen::from_dense(vec![s.clone()], vec![1.0, 2.0])?;
let init_tensor = TensorDynLen::from_dense(vec![s.clone()], vec![0.0, 0.0])?;

let operator = TreeTN::<TensorDynLen, usize>::from_tensors(vec![operator_tensor], vec![0])?;
let rhs = TreeTN::<TensorDynLen, usize>::from_tensors(vec![rhs_tensor], vec![0])?;
let init = TreeTN::<TensorDynLen, usize>::from_tensors(vec![init_tensor], vec![0])?;

let result = square_linsolve(&operator, &rhs, init, &0usize, LinsolveOptions::default(), None, None)?;
assert_eq!(result.solution.node_count(), 1);