7. UniTensor

Besides the generic Tensor structure, Cytnx provides further objects that are designed specifically for tensor network simulations, based on the cytnx.Tensor class.

UniTensor is an enhanced version of cytnx.Tensor which provides features such as labels for each index (which we call “bond”) and Bra/Ket (In/Out) convention of bonds. These features are handy for contractions of multiple tensors, as well as for the implementation of ensor network diagrams. Also, symmetries can be included.

A UniTensor consist of three important parts:

1. Block(s), which is a cytnx.Tensor (or a list/vector thereof). Block(s) store all the elements of the tensor.

2. Bonds, which contain the information associated to each index of the tensor.

3. Labels, which give each bond a name by which it can be accessed.

In the simplest case where no symmetries of the system are considered, a UniTensor can be thought of as adding the meta data bonds and labels to a cytnx.Tensor. A UniTensor can be constructed with a Bond object, or directly from a cytnx.Tensor which gets converted to a UniTensor.

In the following, let’s look into these objects:

• 7.1. Print and display
  • 7.1.1. print_diagram()
  • 7.1.2. print() and print_blocks()
  • 7.1.3. print_block()
• 7.2. Creating a UniTensor
  • 7.2.1. Constructing from Tensor
  • 7.2.2. From scratch
    • UniTensor()
  • 7.2.3. Type conversion
  • 7.2.4. Transfer between devices
  • 7.2.5. Tagged UniTensors and UniTensors with Symmetries
• 7.3. Changing labels
  • UniTensor.relabel_()
  • UniTensor.relabel_()
  • UniTensor.relabels_()
  • UniTensor.relabels_()
  • 7.3.1. Creating UniTensors with different labels that share data
• 7.4. Bond
  • Bond()
  • 7.4.1. Symmetry object
  • 7.4.2. Creating Bonds with quantum numbers
    • Bond()
    • Bond()
  • 7.4.3. Combining Bonds
• 7.5. Tagged UniTensor
  • 7.5.1. Non-symmetric Tagged UniTensor
• 7.6. UniTensor with Symmetries
• 7.7. Accessing the block(s)
  • 7.7.1. UniTensor without symmetries
  • 7.7.2. UniTensor with symmetries
    • UniTensor.get_block()
    • UniTensor.get_block()
  • 7.7.3. Putting a block
    • UniTensor.put_block()
    • UniTensor.put_block()
• 7.8. Get/set UniTensor element
  • 7.8.1. UniTensor without symmetries
  • 7.8.2. UniTensor with symmetries
• 7.9. Manipulate UniTensor
  • 7.9.1. Permute
  • 7.9.2. Reshape
  • 7.9.3. Combine bonds
    • UniTensor.combineBonds()
  • 7.9.4. Arithmetic
  • 7.9.5. Rowrank
  • 7.9.6. Transpose
• 7.10. Save/Load a UniTensor
  • 7.10.1. Save a UniTensor
  • 7.10.2. Load a UniTensor