v0.4.1

PEPSKit v0.4.1

Diff since v0.4.0

Merged pull requests:

• Update correlation_length implementation (#123) (@leburgel)
• Adapt simple update to DiagonalTensorMap (#124) (@Yue-Zhengyuan)
• Refactor boundary MPS contractions to directly use MPSKit.InfiniteMPO (#125) (@leburgel)