From 5639974b67ab7e677cfbf12cb70b28a0e1b58cc3 Mon Sep 17 00:00:00 2001
From: Tony S Yu <tsyu80@gmail.com>
Date: Sat, 1 Sep 2012 17:43:51 -0400
Subject: [PATCH 1/4] BUG: Fix streamplot when velocity component is exactly
 zero.

---
 lib/matplotlib/streamplot.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/matplotlib/streamplot.py b/lib/matplotlib/streamplot.py
index a3a349a74fee..8022f7d3fc93 100644
--- a/lib/matplotlib/streamplot.py
+++ b/lib/matplotlib/streamplot.py
@@ -461,14 +461,14 @@ def _euler_step(xf_traj, yf_traj, dmap, f):
     xi = xf_traj[-1]
     yi = yf_traj[-1]
     cx, cy = f(xi, yi)
-    if cx > 0:
-        dsx = (nx - 1 - xi) / cx
-    else:
+    if cx < 0:
         dsx = xi / -cx
-    if cy > 0:
-        dsy = (ny - 1 - yi) / cy
     else:
+        dsx = (nx - 1 - xi) / cx
+    if cy < 0:
         dsy = yi / -cy
+    else:
+        dsy = (ny - 1 - yi) / cy
     ds = min(dsx, dsy)
     xf_traj.append(xi + cx*ds)
     yf_traj.append(yi + cy*ds)

From 4bbd6715aef2df137da8de85cf0e4a1a25316349 Mon Sep 17 00:00:00 2001
From: Tony S Yu <tsyu80@gmail.com>
Date: Sun, 2 Sep 2012 08:42:41 -0400
Subject: [PATCH 2/4] Catch divide-by-zero in _euler_step

---
 lib/matplotlib/streamplot.py | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/lib/matplotlib/streamplot.py b/lib/matplotlib/streamplot.py
index 8022f7d3fc93..2c2d707787ca 100644
--- a/lib/matplotlib/streamplot.py
+++ b/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

From 0d7a1d1c56167446195c37f43c3dbce20ab32278 Mon Sep 17 00:00:00 2001
From: Tony S Yu <tsyu80@gmail.com>
Date: Sun, 2 Sep 2012 08:43:44 -0400
Subject: [PATCH 3/4] Catch divide-by-zero in step calculation

---
 lib/matplotlib/streamplot.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/matplotlib/streamplot.py b/lib/matplotlib/streamplot.py
index 2c2d707787ca..205b22a11798 100644
--- a/lib/matplotlib/streamplot.py
+++ b/lib/matplotlib/streamplot.py
@@ -450,7 +450,10 @@ def _integrate_rk12(x0, y0, dmap, f):
             stotal += ds
 
         # recalculate stepsize based on step error
-        ds = min(maxds, 0.85 * ds * (maxerror/error)**0.5)
+        if error == 0:
+            ds = maxds
+        else:
+            ds = min(maxds, 0.85 * ds * (maxerror/error)**0.5)
 
     return stotal, xf_traj, yf_traj
 

From 1d4682cec318cfb909b6de5370feb7e8d0657a81 Mon Sep 17 00:00:00 2001
From: Tony S Yu <tsyu80@gmail.com>
Date: Sun, 2 Sep 2012 08:52:59 -0400
Subject: [PATCH 4/4] Prevent warning with masked array inputs

---
 lib/matplotlib/streamplot.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/matplotlib/streamplot.py b/lib/matplotlib/streamplot.py
index 205b22a11798..43d2d79daea3 100644
--- a/lib/matplotlib/streamplot.py
+++ b/lib/matplotlib/streamplot.py
@@ -325,7 +325,7 @@ def get_integrator(u, v, dmap, minlength):
     # speed (path length) will be in axes-coordinates
     u_ax = u / dmap.grid.nx
     v_ax = v / dmap.grid.ny
-    speed = np.sqrt(u_ax**2 + v_ax**2)
+    speed = np.ma.sqrt(u_ax**2 + v_ax**2)
 
     def forward_time(xi, yi):
         ds_dt = interpgrid(speed, xi, yi)