Add example of the proposed solution for the delay differential equat…

…ion issue #1.

dde_example.py

@@ -0,0 +1,35 @@
+import numpy as np
+from ddeint import ddeint
+from pylab import array, sin, linspace, subplots
+
+tau = 30.0
+
+
+def foo(t):
+    if t < 10.0:
+        return 0.0
+    elif 10.0 <= t < 10.0 * np.pi:
+        return 1.0
+    else:
+        return 10.0 * sin(t * 0.5)
+
+
+def values_before_zero(t):
+    return array([0.0, 0.0])
+
+
+def model(Y, t):
+    x, y = Y(t)
+    x_tau, y_tau = Y(t - tau)
+    return array([foo(t), x_tau])
+
+
+tt = linspace(0, 100, 1000)
+yy = ddeint(model, values_before_zero, tt)
+
+fig, ax = subplots(1, figsize=(8, 4))
+
+ax.plot(tt, [x[0] for x in yy], label="trace1")
+ax.plot(tt, [x[1] for x in yy], label="trace2")
+fig.legend(loc='upper center', borderaxespad=2.0)
+fig.show()