From 654115338ddc4cbf57eb68fb33a13393f704a0cd Mon Sep 17 00:00:00 2001
From: peppelauro <peppe.lauro@gmail.com>
Date: Wed, 21 Nov 2018 14:44:12 +0100
Subject: [PATCH 1/3] Added erfcinv

Add function erfcinv (Inverse Complementary Error Function)
---
 pyerf/pyerf.py | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/pyerf/pyerf.py b/pyerf/pyerf.py
index 941f788..f54dc81 100644
--- a/pyerf/pyerf.py
+++ b/pyerf/pyerf.py
@@ -342,6 +342,43 @@ def erfinv(z):
     # otherwise calculate things.
     return _ndtri((z + 1) / 2.0) / math.sqrt(2)
 
+def erfcinv(z):
+    """
+    Calculate the inverse complementary error function at point ``z``.
+    
+    Parameters
+    ----------
+    z : numeric
+
+    Returns
+    -------
+    float
+
+    References
+    ----------
+    + https://en.wikipedia.org/wiki/Error_function#Inverse_functions
+    + http://functions.wolfram.com/GammaBetaErf/InverseErfc/
+
+    Examples
+    --------
+    >>> round(erfcinv(0.1), 12)
+    1.163087153677
+    >>> round(erfcinv(0.5), 12)
+    0.476936276204    
+    >>> round(erfcinv(0.95), 12)
+    0.04434038791
+    >>> round(erfc(erfcinv(1.9)), 12)
+    -1.163087153677    
+    """
+    if abs(z) > 1:
+        raise ValueError("`z` must be between 0 and 2")
+
+    # Shortcut special cases
+    if z == 0:
+        return 0
+    
+    # otherwise calculate things.
+    return -_ndtri(0.5 * z) / math.sqrt(2)
 
 # bring the built-ins into this namespace for conveinence.
 try:

From 3e38ecef3356ed91884103a161952494565b5007 Mon Sep 17 00:00:00 2001
From: peppelauro <peppe.lauro@gmail.com>
Date: Wed, 21 Nov 2018 17:18:57 +0100
Subject: [PATCH 2/3] Update pyerf.py

---
 pyerf/pyerf.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/pyerf/pyerf.py b/pyerf/pyerf.py
index f54dc81..023fe2c 100644
--- a/pyerf/pyerf.py
+++ b/pyerf/pyerf.py
@@ -370,11 +370,13 @@ def erfcinv(z):
     >>> round(erfc(erfcinv(1.9)), 12)
     -1.163087153677    
     """
-    if abs(z) > 1:
-        raise ValueError("`z` must be between 0 and 2")
+    if z < 0 or z > 2:
+        raise ValueError("`z` must be between 0 and 2 inclusive")
 
     # Shortcut special cases
     if z == 0:
+        return inf
+    if z == 1:
         return 0
     
     # otherwise calculate things.

From a8cd206786e5a97f4de5058fd6f91c287062fcff Mon Sep 17 00:00:00 2001
From: peppelauro <peppe.lauro@gmail.com>
Date: Wed, 21 Nov 2018 17:22:48 +0100
Subject: [PATCH 3/3] Update pyerf.py

---
 pyerf/pyerf.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pyerf/pyerf.py b/pyerf/pyerf.py
index 023fe2c..7bd6d8b 100644
--- a/pyerf/pyerf.py
+++ b/pyerf/pyerf.py
@@ -368,7 +368,7 @@ def erfcinv(z):
     >>> round(erfcinv(0.95), 12)
     0.04434038791
     >>> round(erfc(erfcinv(1.9)), 12)
-    -1.163087153677    
+    1.9
     """
     if z < 0 or z > 2:
         raise ValueError("`z` must be between 0 and 2 inclusive")