Enum IndexDirection 

pub enum IndexDirection {
    Derivative,
    Batch,
    Output,
    Input,
}

IndexDirection represents a tensor’s leg direction from the quantum circuit perspective.

In the context of quantum circuits and tensor networks, indices (or “legs”) of a tensor are categorized by their direction to signify their role in an operation.

While tensors may conceptually have multiple indices (legs), in the qudit-expr library, TensorExpression objects are always generated as 1-D, 2-D, or 3-D tensors. This enum links the conceptual/graphical tensor indices to the generated expression’s dimensions by grouping them along directions. So all Input, Output, and Batch legs correspond to a specific dimension of the generated tensor. This tensor network library can use this to predict and manipulate the shape of a generated tensor.

For example, kets capture quantum states, and are represented conceptually by column vectors. In the tensor network perspective, they are represented by a tensor with only Output indices. They have as many indices as there are qudits in the state and the size of each index is the radix of the qudit. For qubits, the radix is 2, so all indices would have dimension 2. However, when generated in the qudit-expr library, they are generated as a vector. The IndexDirection is what is used by the qudit-tensor library to expect a vector shape, since a ket tensor will only have indices in one direction.

Similarly, gates which capture quantum operations, are represented by unitary matrices. As a tensor, they have indices that point in both Input and Output directions. Even though there will likely be more than 2 indices, the qudit-tensor library expects a matrix to be generated by the underlying TensorExpression because of the two distinct directions.

Batch indices are used for measurements/Kraus operators or for batch executions of a network.

Variants

Derivative

For gradients and hessians

Batch

Batch index of a tensor. These are typically represented in quantum circuits through interactions with classical systems through measurements and/or feed-forward operations. Additionally, they can capture batch computations of a network.

Output

Output leg of a tensor, corresponds to rows of an operation. In circuit diagrams, these represent the wires leaving a gate or ket.

Input

Input leg of a tensor, corresponds to columns of an operation. In circuit diagrams, these represent the wires going into a gate or bra.

Implementations

impl IndexDirection

pub fn is_derivative(&self) -> bool

pub fn is_batch(&self) -> bool

pub fn is_output(&self) -> bool

pub fn is_input(&self) -> bool

Trait Implementations

impl Clone for IndexDirection

fn clone(&self) -> IndexDirection

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for IndexDirection

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for IndexDirection

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Hash for IndexDirection

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for IndexDirection

fn cmp(&self, other: &IndexDirection) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for IndexDirection

fn eq(&self, other: &IndexDirection) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for IndexDirection

fn partial_cmp(&self, other: &IndexDirection) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Copy for IndexDirection

impl Eq for IndexDirection

impl StructuralPartialEq for IndexDirection