## 📄️ Simulators

Sometimes when we assemble algorithms, it is useful to check whether or not the resulting state is consistent with our expectation. As the state is not something we have access to with experiment, we need to use a simulator to obtain the exact final output state. In QURI Parts, a simulator is any function that work with the explicit state vector or density matrices.

## 🗃️ Parametric

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## 📄️ Variational algorithms

Recently, variational quantum algorithms are actively studied, where optimal values of parameters in parametric quantum circuits are searched. In this section, we see how to construct one of the variational algorithms, variational quantum eigensolver (VQE), using the gradient.