ndarray-opteinsum

ndarray-opteinsum

N-ary einsum frontend for ndarray arrays, powered by strided-opteinsum.

Scope

• Thin wrapper over strided-opteinsum that accepts ndarray ArrayD<T> and ArrayViewD<T> types directly
• Direct dims/strides passthrough (no notation reversal needed, unlike mdarray-opteinsum)
• Supports negative strides (reversed views)
• einsum() returns an owned ArrayD<T>; einsum_into() writes into a pre-allocated ArrayViewMutD
• Supports f64 and Complex64 operands

Quick Example

use ndarray::ArrayD;
use ndarray_opteinsum::einsum;

// Row-major 2x3 and 3x2 matrices
let a = ArrayD::from_shape_vec(vec![2, 3], vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0]).unwrap();
let b = ArrayD::from_shape_vec(vec![3, 2], vec![7.0, 8.0, 9.0, 10.0, 11.0, 12.0]).unwrap();

// Matrix multiplication
let c: ArrayD<f64> = einsum("ij,jk->ik", vec![(&a).into(), (&b).into()]).unwrap();

How It Works

ndarray has explicit strides (&[isize], element-based) matching StridedView's convention, so dims and strides are passed through directly without any reversal.

• Input conversion: Zero-copy wrapping of ndarray pointers, shapes, and strides as StridedView
• Negative strides: Supported via offset calculation (compute_offset_range)
• einsum_into(): Fully copy-free
• einsum(): One copy via copy_into to materialize the result into contiguous row-major order

Comparison with mdarray-opteinsum

	mdarray-opteinsum	ndarray-opteinsum
notation	label reversal required	passthrough
input conversion	reverse dims/strides	direct passthrough
negative strides	N/A	supported
output construction	unsafe from_raw_parts	safe from_shape_vec

API

// Allocating: returns owned ArrayD
pub fn einsum<T: EinsumScalar>(
    notation: &str,
    operands: Vec<NdOperand<'_>>,
) -> Result<ArrayD<T>>

// In-place: output = alpha * einsum(operands) + beta * output
pub fn einsum_into<T: EinsumScalar>(
    notation: &str,
    operands: Vec<NdOperand<'_>>,
    output: &mut ArrayViewMutD<'_, T>,
    alpha: T,
    beta: T,
) -> Result<()>

NdOperand<'a> is constructed via From impls on &ArrayD<T> and ArrayViewD<'a, T>.