- #1

- 89

- 3

## Homework Statement

This is not really a problem but I was going over my lecture notes and I see [itex] \mathscr{H}=\frac{1}{2}\left(\pi^{2} + \vec{\nabla}\phi \cdot \vec{\nabla}\phi + m^{2}\phi^{2}\right) [/itex] and [itex]\frac{\partial\mathscr{H}}{\partial\phi} = -\nabla^{2}\phi + m^{2}\phi [/itex]

## Homework Equations

## The Attempt at a Solution

I would think that [itex]\frac{\partial\mathscr{H}}{\partial\phi} = \nabla^{2}\phi + m^{2}\phi [/itex]. But I don't know where the minus sign is coming from.