PhysicsGente
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Homework Statement
This is not really a problem but I was going over my lecture notes and I see \mathscr{H}=\frac{1}{2}\left(\pi^{2} + \vec{\nabla}\phi \cdot \vec{\nabla}\phi + m^{2}\phi^{2}\right) and \frac{\partial\mathscr{H}}{\partial\phi} = -\nabla^{2}\phi + m^{2}\phi
Homework Equations
The Attempt at a Solution
I would think that \frac{\partial\mathscr{H}}{\partial\phi} = \nabla^{2}\phi + m^{2}\phi. But I don't know where the minus sign is coming from.