VQE supports initialization by computer #263
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Note that on my machine, the newly added test takes about 20 seconds to run. |
src/qforte/abc/algorithm.py
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| raise ValueError("unitary_circ reference must be a Circuit.") | ||
| if not fast: | ||
| raise ValueError( | ||
| "User specified they want to simulate a quantum computer but not specify how to prepare the initial state. That's inconsistent." |
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It is not clear to me how this message relates to the fast keyword.
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If fast is off, the user has specified they want to simulate the full operations as if on a quantum computer. But by supplying a quantum computer, you're skipping a step: state preparation!
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Perhaps the word fast is not the best descriptor for what the code is doing. Of course, this is outside the scope of this PR.
I understand that you want to be precise, but what worries me is that this error message does not reference the fast keyword. The user might not be able to immediately understand what they did to cause this error. For example, in other places of the code, similar error messages read: "self._fast must be True for gradient measurement."
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Easy enough to fix. Are there issues with the new error message?
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The new error message is great! Feel free to merge.
| raise ValueError("Class cannot be initialized with a computer.") | ||
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| self._ref = system.hf_reference | ||
| self._refprep = build_refprep(self._ref) |
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Is _refprep still needed in this case?
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Maybe - it depends on what "this case" is.
If you want to use an excitation-based pool, it's needed. If you want to do PQE, it's needed. If you want to do moment corrections, it's needed. Otherwise, it isn't needed. Giving QForte the infrastructure to skip this step if not needed seemed beyond the scope of the PR.
| coeff_vec = np.zeros(2**nqubits) | ||
| coeff_vec[int("00001111", 2)] = 1 | ||
| coeff_vec[int("00110011", 2)] = 0.2 | ||
| coeff_vec[int("00111100", 2)] = 0.1 | ||
| coeff_vec[int("11001100", 2)] = 0.04 | ||
| coeff_vec /= np.linalg.norm(coeff_vec) | ||
| computer.set_coeff_vec(coeff_vec) |
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As an additional test, would it be possible to check that the initial guess energy agrees with the expectation value of the Hamiltonian with respect to the state generated by the computer?
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The initial guess energy isn't stored on the wavefunction. I could do it, but I'd need to hardcode that value of that initial guess energy.
src/qforte/abc/algorithm.py
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| raise ValueError("unitary_circ reference must be a Circuit.") | ||
| if not fast: | ||
| raise ValueError( | ||
| "User specified they want to simulate a quantum computer but not specify how to prepare the initial state. That's inconsistent." |
There was a problem hiding this comment.
Perhaps the word fast is not the best descriptor for what the code is doing. Of course, this is outside the scope of this PR.
I understand that you want to be precise, but what worries me is that this error message does not reference the fast keyword. The user might not be able to immediately understand what they did to cause this error. For example, in other places of the code, similar error messages read: "self._fast must be True for gradient measurement."
Description
Addresses a major use case of #168 - VQE now allows the user to pass in a computer to initialize the state.
User Notes
Computer.Checklist