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Divergence and curl

Problem 12.105 · easy

Find the divergence and curl of \( \displaystyle \mathbf{F} = \langle 3 z^{2}, 3 z^{2}, \sin{\left(y \right)} \rangle \).

\[ \frac{d}{d x} 3 z^{2} + \frac{d}{d y} 3 z^{2} + \frac{d}{d z} \sin{\left(y \right)} = 0 \]
div F.✓ Proved
\[ \left[\begin{matrix}- \frac{d}{d z} 3 z^{2} + \frac{d}{d y} \sin{\left(y \right)}\\\frac{d}{d z} 3 z^{2} - \frac{d}{d x} \sin{\left(y \right)}\\\frac{d}{d x} 3 z^{2} - \frac{d}{d y} 3 z^{2}\end{matrix}\right] = \left[\begin{matrix}- 6 z + \cos{\left(y \right)}\\6 z\\0\end{matrix}\right] \]
curl F, component by component.✓ Proved

Answer \( \nabla\cdot\mathbf{F} = 0,\quad \nabla\times\mathbf{F} = \langle - 6 z + \cos{\left(y \right)}, 6 z, 0 \rangle \)

Every line of this solution was proved by the computer algebra system SymPy. The answer was also checked a second way, without looking at the solution. The reviewers disagree about how one step is explained; every verdict is in the receipt.

The full receipt

Line	Status	Checked by	Detail
1	✓ Proved	sympy 1.14.0	simplify(lhs - rhs) reduced to 0
2	✓ Proved	sympy 1.14.0	simplify(lhs - rhs) reduced to 0
answer, a second way	✓ Checked independently	sympy 1.14.0 + mpmath 1.3.0	difference quotients of each component at (0.3, 0.7, 1.1) agree

Reviewers

gpt-oss:20b: pass
qwen3.6:27b-mlx: fail (error) — The stated answer is a 4x1 matrix, but the divergence and curl of a 3D vector field should result in a scalar and a 3D vector, respectively. The solution correctly computes the components but fails to present them in the standard format or explain the discrepancy with the stated answer's shape.

Every verdict on record (4)

qwen3.6:27b-mlx: fail (error) 2026-09-26 — The stated answer is a 4x1 matrix, but the divergence and curl of a 3D vector field should result in a scalar and a 3D vector, respectively. The solution correctly computes the components but fails to present them in the standard format or explain the discrepancy with the stated answer's shape.
gpt-oss:20b: pass 2026-09-26
qwen3.6:27b-mlx: fail (error) 2026-09-26 — The stated answer is a 4x1 matrix, but the divergence and curl of a 3D vector field are a scalar and a 3D vector, respectively. The solution computes them correctly but fails to present them in the standard format or explain the mismatch with the provided 'stated answer'.
gpt-oss:20b: pass 2026-09-26

Proved: SymPy reduced the difference between the two sides to zero. Checked independently: a separate method, named above, confirmed it. Checked numerically: the two sides agree at every sampled point, which is evidence, not proof. Reviewed: a model or a person read it; that is all a sentence can have. Solution by generator:structured/divergence_curl, checked 2026-09-26 with SymPy 1.14.0.