Catch divide-by-zero in _euler_step

Author: tonysyu

lib/matplotlib/streamplot.py

@@ -456,16 +456,20 @@ def _integrate_rk12(x0, y0, dmap, f):
 
 
 def _euler_step(xf_traj, yf_traj, dmap, f):
-    """Simple Euler integration step."""
+    """Simple Euler integration step that extends streamline to boundary."""
     ny, nx = dmap.grid.shape
     xi = xf_traj[-1]
     yi = yf_traj[-1]
     cx, cy = f(xi, yi)
-    if cx < 0:
+    if cx == 0:
+        dsx = np.inf
+    elif cx < 0:
         dsx = xi / -cx
     else:
         dsx = (nx - 1 - xi) / cx
-    if cy < 0:
+    if cy == 0:
+        dsy = np.inf
+    elif cy < 0:
         dsy = yi / -cy
     else:
         dsy = (ny - 1 - yi) / cy