Update fluidEm3d-demo.md

demos/fluidEm3d-demo.md

@@ -1,22 +1,5 @@
 
-
-```python
-"""
-DEMO: Waves in a cold plasma
-"""
-
-import matplotlib.pyplot as plt
-import numpy as np
-plt.rcParams['axes.labelsize'] = 'xx-large'
-plt.rcParams['axes.titlesize'] = 'xx-large'
-
-import sys
-sys.path.append('/path/to/xeon')
-sys.path.append('/home/liang/src')
-import xeon
-```
-
-### Magnetized cold overdense ($\omega_{pe}>\Omega_{ce}$) plasma
+### Waves in a magnetized cold, overdense ($\omega_{pe}>\Omega_{ce}$) plasma
 #### Parallel propagation
 - Plasma oscillation
 - Electron cyclotron wave == Whistler wave; right-handed circularly polarized; Compressional Alfven wave
@@ -29,12 +12,26 @@ import xeon
 #### Low-frequency limit
 - Shear or slow-Alfven wave, $\omega=\frac{kv_A\cos\theta}{\sqrt{1+v_A^2/c^2}}\approx k\cos\theta v_A=k_\parallel v_A$
 - Compressional or fast-Alfven wave $\omega=\frac{kv_A}{\sqrt{1+v_A^2/c^2}}\approx kv_A$
-
 - At $\theta=0$, the compressional and shear Alfven waves are indistiguishable.
 - The shear Alfven wave cannot propagate at $\theta=90^\circ$
 
 
 ```python
+
+```python
+"""
+DEMO: Waves in a cold plasma
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+plt.rcParams['axes.labelsize'] = 'xx-large'
+plt.rcParams['axes.titlesize'] = 'xx-large'
+
+import sys
+sys.path.append('/path/to/xeon')
+import xeon
+
 # magnetized plasma, angle between k and Bz0 from 0 to pi/2
 
 B0 = 0.8