# Exercise V.2.3: Variational Quantum Eigensolver Codebook

**URL:** <https://discuss.pennylane.ai/t/exercise-v-2-3-variational-quantum-eigensolver-codebook/7707>\
**Category:** Codebook\
**Created:** [December 9, 2024, 3:42pm UTC](https://discuss.pennylane.ai/t/exercise-v-2-3-variational-quantum-eigensolver-codebook/7707 "2024-12-09T15:42:29Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![jsgs8skwkw](https://avatars.discourse-cdn.com/v4/letter/j/5fc32e/32.png) [@jsgs8skwkw](https://discuss.pennylane.ai/u/jsgs8skwkw)\
**Post date:** [December 9, 2024, 3:42pm UTC](https://discuss.pennylane.ai/t/exercise-v-2-3-variational-quantum-eigensolver-codebook/7707/1 "2024-12-09T15:42:29Z")

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In Exercise V.2.3., may be there is an error of |ψ\>=(0,1/√2,-1/√2,0)T? It should be (0,-1/√2,1/√2,0)T indead. Please check, I try to calculate the result of the circuit in the encloser.

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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:** [December 10, 2024, 12:07am UTC](https://discuss.pennylane.ai/t/exercise-v-2-3-variational-quantum-eigensolver-codebook/7707/2 "2024-12-10T00:07:36Z")

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Hi @jsgs8skwkw , welcome to the Forum!

I think you might be right. Both of these states are eigenstates corresponding to the -2 eigenvalue, but the circuit is actually implementing [0,\frac{-1}{\sqrt2},\frac{1}{\sqrt2},0]^T.

We will work on fixing this. Thank you for pointing it out!