add support for adam

README.md

@@ -40,5 +40,4 @@ print(y.grad)  # dz/dy
 
 * Implement gradcheck (numeric)
 * Implement convolutions
-* Implement Adam optimizer
 

test/mnist.py

@@ -28,6 +28,7 @@ class TinyBobNet:
 
 model = TinyBobNet()
 optim = optim.SGD([model.l1, model.l2], lr=0.01)
+#optim = optim.Adam([model.l1, model.l2], lr=0.001)
 
 BS = 128
 losses, accuracies = [], []
@@ -51,7 +52,6 @@ for i in (t := trange(1000)):
   cat = np.argmax(outs.data, axis=1)
   accuracy = (cat == Y).mean()
   
-  
   # printing
   loss = loss.data
   losses.append(loss)

tinygrad/optim.py

@@ -1,9 +1,37 @@
-class SGD:
-  def __init__(self, tensors, lr):
-    self.tensors = tensors
+import numpy as np
+
+class Optimizer:
+  def __init__(self, params):
+    self.params = params
+
+class SGD(Optimizer):
+  def __init__(self, params, lr=0.001):
+    super(SGD, self).__init__(params)
     self.lr = lr
 
   def step(self):
-    for t in self.tensors:
+    for t in self.params:
       t.data -= self.lr * t.grad
 
+# 80% sure this is right?
+class Adam(Optimizer):
+  def __init__(self, params, lr=0.001, b1=0.9, b2=0.999, eps=1e-8):
+    super(Adam, self).__init__(params)
+    self.lr = lr
+    self.b1 = b1
+    self.b2 = b2
+    self.eps = eps
+    self.t = 0
+
+    self.m = [np.zeros_like(t.data) for t in self.params]
+    self.v = [np.zeros_like(t.data) for t in self.params]
+
+  def step(self):
+    for i,t in enumerate(self.params):
+      self.t += 1
+      self.m[i] = self.b1 * self.m[i] + (1 - self.b1) * t.grad
+      self.v[i] = self.b2 * self.v[i] + (1 - self.b2) * np.square(t.grad)
+      mhat = self.m[i] / (1. - self.b1**self.t)
+      vhat = self.v[i] / (1. - self.b2**self.t)
+      t.data -= self.lr * mhat / (np.sqrt(vhat) + self.eps)
+