Add discrete_colour_ramp.py

plots/README.md

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+# plots
+
+## discrete_colour_ramp.py
+
+![discrete colour ramp](png/discrete-colour-ramp.png)

plots/discrete_colour_ramp.py

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+import os
+import numpy as np
+import matplotlib.pyplot as plt
+
+# Generate dummy data
+delta = 0.01
+x = np.arange(-3.0, 3.0, delta)
+y = np.arange(-3.0, 3.0, delta)
+X, Y = np.meshgrid(x, y)
+Z = X * Y
+
+# Set range and steps for colour bar
+c_max = 8
+c_min = -8
+c_step = 2
+
+# Create colour map
+cmap = plt.cm.get_cmap('Blues', (c_max - c_min + c_step) / c_step)
+
+fig, ax = plt.subplots(1, 1, figsize=(6, 4))
+
+# Plot image
+im = ax.imshow(Z,
+               cmap=cmap,
+               interpolation='bilinear',
+               vmax=c_max + c_step / 2,
+               vmin=c_min - c_step / 2)
+
+# Add colour bar
+plt.colorbar(im, ticks=np.arange(c_min, c_max + 1, c_step))
+
+# Hide spines and ticks
+ax.set_axis_off()
+
+# Export figure
+png_name = os.path.join(
+    'png',
+    os.path.basename(__file__).replace('.py', '.png').replace('_', '-'))
+plt.savefig(png_name, bbox_inches='tight', dpi=100)