Add sub, neg and log methods to pygrad.tensor

pygrad/tensor.py

@@ -36,6 +36,16 @@ class Tensor:
     tensor._back = back
     return tensor
 
+  def sub(self, other):
+    tensor = Tensor(np.add(self.value, other.value))
+    tensor._save(self, other)
+
+    def back(upstream):
+      return np.dot(np.ones_like(self.value).T, upstream), -np.dot(np.ones_like(self.value).T, upstream)
+
+    tensor._back = back
+    return tensor
+
   def mul(self, other):
     tensor = Tensor(np.dot(self.value, other.value))
     tensor._save(self, other)
@@ -58,6 +68,16 @@ class Tensor:
     tensor._back = back
     return tensor
 
+  def neg(self):
+    tensor = Tensor(-self.value)
+    tensor._save(self)
+
+    def back(upstream):
+      return [np.dot(-np.ones_like(self.value), upstream)]
+
+    tensor._back = back
+    return tensor
+
   def expt(self, exponent):
     tensor = Tensor(self.value ** exponent)
     tensor._save(self)
@@ -91,6 +111,17 @@ class Tensor:
     tensor._back = back
     return tensor
 
+  def log(self):
+    tensor = Tensor(np.log(self.value))
+    tensor._save(self)
+
+    def back(upstream):
+      a, = tensor._parents
+      return [np.dot(1 / a.value, upstream)]
+
+    tensor._back = back
+    return tensor
+
   def tanh(self):
     tensor = Tensor(np.tanh(self.value))
     tensor._save(self)