From 85d16f81a93bdde2287e39dc61df9dc6ddb108a5 Mon Sep 17 00:00:00 2001
From: Niru Maheswaranathan <nirum@stanford.edu>
Date: Mon, 7 Sep 2015 02:20:54 -0500
Subject: [PATCH] Adds soft rectification function

---
 jetpack/signals.py | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/jetpack/signals.py b/jetpack/signals.py
index 65124b8..1a9298c 100644
--- a/jetpack/signals.py
+++ b/jetpack/signals.py
@@ -10,7 +10,7 @@
 import numpy as np
 from scipy.ndimage.filters import gaussian_filter1d
 
-__all__ = ['peakdet', 'smooth', 'norms', 'sfthr', 'sq', 'arr']
+__all__ = ['peakdet', 'smooth', 'norms', 'sfthr', 'sfrct', 'sq', 'arr']
 
 
 def peakdet(v, delta, x=None):
@@ -182,6 +182,30 @@ def sfthr(x, threshold):
     return np.sign(x) * np.maximum(np.abs(x) - threshold, 0)
 
 
+def sfrct(x, threshold):
+    """
+    Soft rectification function
+
+    y = log(1 + exp(x - threshold))
+
+    Parameters
+    ----------
+    x : array_like
+        The input array to the soft thresholding function
+
+    threshold : float
+        The threshold of the function
+
+    Returns
+    -------
+    y : array_like
+        The output of the soft thresholding function
+
+    """
+
+    return np.log1p(np.exp(x - threshold))
+
+
 def sq(x):
     """
     Reshape vector to a square image