fixed minus sign

src/5_wigner.md

@@ -4,8 +4,8 @@ jupyter:
     text_representation:
       extension: .md
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-      format_version: '1.0'
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+      format_version: '1.2'
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@@ -55,7 +55,7 @@ $$
 where $p$ is just the 1D scalar momentum, not the momentum operator.  We can also form $W(x,p)$ with $\phi(p)$, the Fourier transform of $\psi(x)$:
 
 $$
-W(x,p) = \frac{1}{\pi \hbar} \int_{-\infty}^{+\infty} \phi^*(p+q) \phi(p-q) e^{2iqx/\hbar} dq
+W(x,p) = \frac{1}{\pi \hbar} \int_{-\infty}^{+\infty} \phi^*(p+q) \phi(p-q) e^{-2iqx/\hbar} dq
 $$
 
 How should we interpret the Wigner function?  It must be something like a probability distribution, as the name suggests.  If we integrate $W(x,p)$ over all $p$, we get $|\psi(x)|^2$: