# Codebook: Introduction to Variational Quantum Algorithms

**URL:** <https://discuss.pennylane.ai/t/codebook-introduction-to-variational-quantum-algorithms/5429>\
**Category:** Codebook\
**Created:** [October 5, 2024, 12:58pm UTC](https://discuss.pennylane.ai/t/codebook-introduction-to-variational-quantum-algorithms/5429 "2024-10-05T12:58:17Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![yoshypdf](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/yoshypdf/32/2818_2.png) [@yoshypdf](https://discuss.pennylane.ai/u/yoshypdf)\
**Post date:** [October 5, 2024, 12:58pm UTC](https://discuss.pennylane.ai/t/codebook-introduction-to-variational-quantum-algorithms/5429/1 "2024-10-05T12:58:18Z")

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Hello,  
I believe there is an error in the formula for the commutator of P and B. It should also include a second term with U^dag(-pi/2)BU(-pi/2).

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**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\
**Post date:** [October 9, 2024, 2:29am UTC](https://discuss.pennylane.ai/t/codebook-introduction-to-variational-quantum-algorithms/5429/2 "2024-10-09T02:29:34Z")

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Hi @yoshypdf ,

Great catch!  
Thank you for helping us make the Codebook better! 🙌