added logexp_clipped transformation

GPy/core/transformations.py

@@ -38,6 +38,23 @@ class logexp(transformation):
     def __str__(self):
         return '(+ve)'
 
+class logexp_clipped(transformation):
+    def __init__(self):
+        self.domain = 'positive'
+    def f(self, x):
+        f = np.log(1. + np.exp(x))
+        return f
+    def finv(self, f):
+        return np.log(np.exp(f) - 1.)
+    def gradfactor(self, f):
+        ef = np.exp(f)
+        gf = (ef - 1.) / ef
+        return np.where(f < 1e-6, 0, gf)
+    def initialize(self, f):
+        return np.abs(f)
+    def __str__(self):
+        return '(+ve)'
+
 class exponent(transformation):
     def __init__(self):
         self.domain = 'positive'
@@ -66,6 +83,20 @@ class negative_exponent(transformation):
     def __str__(self):
         return '(-ve)'
 
+class square(transformation):
+    def __init__(self):
+        self.domain = 'positive'
+    def f(self, x):
+        return x ** 2
+    def finv(self, x):
+        return np.sqrt(x)
+    def gradfactor(self, f):
+        return 2 * np.sqrt(f)
+    def initialize(self, f):
+        return np.abs(f)
+    def __str__(self):
+        return '(+sq)'
+
 class logistic(transformation):
     def __init__(self, lower, upper):
         self.domain = 'bounded'