觉得 solver.py 拿来训练很好用，存一波：
目录：solver.py ， solver训练FullyConnectedNet ， 外加一段可视化loss与accuracy函数的代码 。
solver.py:
from __future__ import print_function, division
from builtins import range
from builtins import object
import os
import pickle as pickle
import numpy as np
from cs231n import optim #这个 optim 文件内容就是各种 update_rules
class Solver(object):
"""
A Solver encapsulates all the logic necessary for training classification
models. The Solver performs stochastic gradient descent using different
update rules defined in optim.py.
The solver accepts both training and validataion data and labels so it can
periodically check classification accuracy on both training and validation
data to watch out for overfitting.
To train a model, you will first construct a Solver instance, passing the
model, dataset, and various optoins (learning rate, batch size, etc) to the
constructor. You will then call the train() method to run the optimization
procedure and train the model.
After the train() method returns, model.params will contain the parameters
that performed best on the validation set over the course of training.
In addition, the instance variable solver.loss_history will contain a list
of all losses encountered during training and the instance variables
solver.train_acc_history and solver.val_acc_history will be lists of the
accuracies of the model on the training and validation set at each epoch.
Example usage might look something like this:
data = {
'X_train': # training data
'y_train': # training labels
'X_val': # validation data
'y_val': # validation labels
}
model = MyAwesomeModel(hidden_size=100, reg=10)
solver = Solver(model, data,
update_rule='sgd',
optim_config={
'learning_rate': 1e-3,
},
lr_decay=0.95,
num_epochs=10, batch_size=100,
print_every=100)
solver.train()
A Solver works on a model object that must conform to the following API:
- model.params must be a dictionary mapping string parameter names to numpy
arrays containing parameter values.
- model.loss(X, y) must be a function that computes training-time loss and
gradients, and test-time classification scores, with the following inputs
and outputs:
Inputs:
- X: Array giving a minibatch of input data of shape (N, d_1, ..., d_k)
- y: Array of labels, of shape (N,) giving labels for X where y[i] is the
label for X[i].
Returns:
If y is None, run a test-time forward pass and return:
- scores: Array of shape (N, C) giving classification scores for X where
scores[i, c] gives the score of class c for X[i].
If y is not None, run a training time forward and backward pass and
return a tuple of:
- loss: Scalar giving the loss
- grads: Dictionary with the same keys as self.params mapping parameter
names to gradients of the loss with respect to those parameters.
"""
def __init__(self, model, data, **kwargs):
"""
Construct a new Solver instance.
Required arguments:
- model: A model object conforming to the API described above
- data: A dictionary of training and validation data containing:
'X_train': Array, shape (N_train, d_1, ..., d_k) of training images
'X_val': Array, shape (N_val, d_1, ..., d_k) of validation images
'y_train': Array, shape (N_train,) of labels for training images
'y_val': Array, shape (N_val,) of labels for validation images
Optional arguments:
- update_rule: A string giving the name of an update rule in optim.py.
Default is 'sgd'.
- optim_config: A dictionary containing hyperparameters that will be
passed to the chosen update rule. Each update rule requires different
hyperparameters (see optim.py) but all update rules require a
'learning_rate' parameter so that should always be present.
- lr_decay: A scalar for learning rate decay; after each epoch the
learning rate is multiplied by this value.
- batch_size: Size of minibatches used to compute loss and gradient
during training.
- num_epochs: The number of epochs to run for during training.
- print_every: Integer; training losses will be printed every
print_every iterations.
- verbose: Boolean; if set to false then no output will be printed
during training.
- num_train_samples: Number of training samples used to check training
accuracy; default is 1000; set to None to use entire training set.
- num_val_samples: Number of validation samples to use to check val
accuracy; default is None, which uses the entire validation set.
- checkpoint_name: If not None, then save model checkpoints here every
epoch.
"""
self.model = model
self.X_train = data['X_train']
self.y_train = data['y_train']
self.X_val = data['X_val']
self.y_val = data['y_val']
# Unpack keyword arguments
self.update_rule = kwargs.pop('update_rule', 'sgd')
self.optim_config = kwargs.pop('optim_config', {})
self.lr_decay = kwargs.pop('lr_decay', 1.0)
self.batch_size = kwargs.pop('batch_size', 100)
self.num_epochs = kwargs.pop('num_epochs', 10)
self.num_train_samples = kwargs.pop('num_train_samples', 1000)
self.num_val_samples = kwargs.pop('num_val_samples', None)
self.checkpoint_name = kwargs.pop('checkpoint_name', None)
self.print_every = kwargs.pop('print_every', 10)
self.verbose = kwargs.pop('verbose', True)
# Throw an error if there are extra keyword arguments
if len(kwargs) > 0:
extra = ', '.join('"%s"' % k for k in list(kwargs.keys()))
raise ValueError('Unrecognized arguments %s' % extra)
# Make sure the update rule exists, then replace the string
# name with the actual function
if not hasattr(optim, self.update_rule):
raise ValueError('Invalid update_rule "%s"' % self.update_rule)
self.update_rule = getattr(optim, self.update_rule)
self._reset()
def _reset(self):
"""
Set up some book-keeping variables for optimization. Don't call this
manually.
"""
# Set up some variables for book-keeping
self.epoch = 0
self.best_val_acc = 0
self.best_params = {}
self.loss_history = []
self.train_acc_history = []
self.val_acc_history = []
# Make a deep copy of the optim_config for each parameter
self.optim_configs = {}
for p in self.model.params:
d = {k: v for k, v in self.optim_config.items()}
self.optim_configs[p] = d
def _step(self):
"""
Make a single gradient update. This is called by train() and should not
be called manually.
"""
# Make a minibatch of training data
num_train = self.X_train.shape[0]
batch_mask = np.random.choice(num_train, self.batch_size)
X_batch = self.X_train[batch_mask]
y_batch = self.y_train[batch_mask]
# Compute loss and gradient
loss, grads = self.model.loss(X_batch, y_batch)
self.loss_history.append(loss)
# Perform a parameter update
for p, w in self.model.params.items():
dw = grads[p]
config = self.optim_configs[p]
next_w, next_config = self.update_rule( w , dw, config)
self.model.params[p] = next_w
self.optim_configs[p] = next_config
def _save_checkpoint(self):
if self.checkpoint_name is None: return
checkpoint = {
'model': self.model,
'update_rule': self.update_rule,
'lr_decay': self.lr_decay,
'optim_config': self.optim_config,
'batch_size': self.batch_size,
'num_train_samples': self.num_train_samples,
'num_val_samples': self.num_val_samples,
'epoch': self.epoch,
'loss_history': self.loss_history,
'train_acc_history': self.train_acc_history,
'val_acc_history': self.val_acc_history,
}
filename = '%s_epoch_%d.pkl' % (self.checkpoint_name, self.epoch)
if self.verbose:
print('Saving checkpoint to "%s"' % filename)
with open(filename, 'wb') as f:
pickle.dump(checkpoint, f)
def check_accuracy(self, X, y, num_samples=None, batch_size=100):
"""
Check accuracy of the model on the provided data.
Inputs:
- X: Array of data, of shape (N, d_1, ..., d_k)
- y: Array of labels, of shape (N,)
- num_samples: If not None, subsample the data and only test the model
on num_samples datapoints.
- batch_size: Split X and y into batches of this size to avoid using
too much memory.
Returns:
- acc: Scalar giving the fraction of instances that were correctly
classified by the model.
"""
# Maybe subsample the data
N = X.shape[0]
if num_samples is not None and N > num_samples:
mask = np.random.choice(N, num_samples)
N = num_samples
X = X[mask]
y = y[mask]
# Compute predictions in batches
num_batches = N // batch_size
if N % batch_size != 0:
num_batches += 1
y_pred = []
for i in range(num_batches):
start = i * batch_size
end = (i + 1) * batch_size
scores = self.model.loss(X[start:end])
y_pred.append(np.argmax(scores, axis=1))
y_pred = np.hstack(y_pred)
acc = np.mean(y_pred == y)
return acc
def train(self):
"""
Run optimization to train the model.
"""
num_train = self.X_train.shape[0]
iterations_per_epoch = max(num_train // self.batch_size, 1)
num_iterations = self.num_epochs * iterations_per_epoch
for t in range(num_iterations):
self._step() #梯度更新
# Maybe print training loss
if self.verbose and t % self.print_every == 0:
print('(Iteration %d / %d) loss: %f' % (
t + 1, num_iterations, self.loss_history[-1]))
# At the end of every epoch, increment the epoch counter and decay
# the learning rate.
epoch_end = (t + 1) % iterations_per_epoch == 0
if epoch_end:
self.epoch += 1
for k in self.optim_configs:
self.optim_configs[k]['learning_rate'] *= self.lr_decay
# Check train and val accuracy on the first iteration, the last
# iteration, and at the end of each epoch.
first_it = (t == 0)
last_it = (t == num_iterations - 1)
if first_it or last_it or epoch_end:
train_acc = self.check_accuracy(self.X_train, self.y_train,
num_samples=self.num_train_samples)
val_acc = self.check_accuracy(self.X_val, self.y_val,
num_samples=self.num_val_samples)
self.train_acc_history.append(train_acc)
self.val_acc_history.append(val_acc)
self._save_checkpoint()
if self.verbose:
print('(Epoch %d / %d) train acc: %f; val_acc: %f' % (
self.epoch, self.num_epochs, train_acc, val_acc))
# Keep track of the best model
if val_acc > self.best_val_acc:
self.best_val_acc = val_acc
self.best_params = {}
for k, v in self.model.params.items():
self.best_params[k] = v.copy()
# At the end of training swap the best params into the model
self.model.params = self.best_params
使用示例：
Solver 训练FullyConnectedNet的案例：
best_model = None
################################################################################
# TODO: Train the best FullyConnectedNet that you can on CIFAR-10. You might #
# batch normalization and dropout useful. Store your best model in the #
# best_model variable. #
################################################################################
hidden_dims = np.array([100,120,120,80])
best_model = FullyConnectedNet( hidden_dims, num_classes=10,
dropout=0, use_batchnorm=True, reg=0.2693,
weight_scale=1e-2, dtype=np.float32, seed=None)
solver = Solver(model = best_model,
data = data,
update_rule = 'sgd_momentum',
optim_config={'learning_rate':2e-4},
lr_decay=1.0,
print_every=10, num_epochs=20,
batch_size=100)
solver.train()
################################################################################
# END OF YOUR CODE #
################################################################################外加一段可视化loss与accuracy函数的代码：
# Run this cell to visualize training loss and train / val accuracy
plt.subplot(2, 1, 1)
plt.title('Training loss')
plt.plot(solver.loss_history, 'o')
plt.xlabel('Iteration')
plt.subplot(2, 1, 2)
plt.title('Accuracy')
plt.plot(solver.train_acc_history, '-o', label='train')
plt.plot(solver.val_acc_history, '-o', label='val')
plt.plot([0.5] * len(solver.val_acc_history), 'k--')
plt.xlabel('Epoch')
plt.legend(loc='lower right')
plt.gcf().set_size_inches(15, 12)
plt.show()