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299 lignes
12 KiB
299 lignes
12 KiB
from __future__ import print_function, division
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from future import standard_library
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standard_library.install_aliases()
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from builtins import range
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from builtins import object
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import os
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import pickle as pickle
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import numpy as np
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from daseCV import optim
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class Solver(object):
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"""
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Solver封装了模型训练所需的所有逻辑。
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Solver使用optim.py中定义好的不同更新规则执行随机梯度下降。
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solver同时接受训练、验证数据和标签的输入，
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它可以定期检查训练和验证数据的分类准确性，监视是否存在过拟合。
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要训练模型，首先要构造一个Solver实例，传递模型、数据集和超参数(learning rate, batch size, etc)。
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然后调用train()方法训练模型。
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训练结束后，经过更新在验证集上优化后的模型参数会保存在model.params中。此外，损失值的
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历史训练信息会保存在solver.loss_history中，还有solver.train_acc_history和
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solver.val_acc_history中会分别保存训练集和验证集在每一次epoch时的模型准确率。
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样例如下：
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data = {
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'X_train': # training data
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'y_train': # training labels
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'X_val': # validation data
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'y_val': # validation labels
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}
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model = MyAwesomeModel(hidden_size=100, reg=10)
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solver = Solver(model, data,
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update_rule='sgd',
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optim_config={
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'learning_rate': 1e-3,
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},
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lr_decay=0.95,
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num_epochs=10, batch_size=100,
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print_every=100)
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solver.train()
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A Solver works on a model object that must conform to the following API:
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- model.params must be a dictionary mapping string parameter names to numpy
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arrays containing parameter values.
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- model.loss(X, y) must be a function that computes training-time loss and
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gradients, and test-time classification scores, with the following inputs
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and outputs:
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Inputs:
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- X: Array giving a minibatch of input data of shape (N, d_1, ..., d_k)
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- y: Array of labels, of shape (N,) giving labels for X where y[i] is the
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label for X[i].
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Returns:
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If y is None, run a test-time forward pass and return:
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- scores: Array of shape (N, C) giving classification scores for X where
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scores[i, c] gives the score of class c for X[i].
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If y is not None, run a training time forward and backward pass and
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return a tuple of:
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- loss: Scalar giving the loss
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- grads: Dictionary with the same keys as self.params mapping parameter
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names to gradients of the loss with respect to those parameters.
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"""
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def __init__(self, model, data, **kwargs):
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"""
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Construct a new Solver instance.
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Required arguments:
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- model: A model object conforming to the API described above
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- data: A dictionary of training and validation data containing:
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'X_train': Array, shape (N_train, d_1, ..., d_k) of training images
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'X_val': Array, shape (N_val, d_1, ..., d_k) of validation images
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'y_train': Array, shape (N_train,) of labels for training images
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'y_val': Array, shape (N_val,) of labels for validation images
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Optional arguments:
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- update_rule: A string giving the name of an update rule in optim.py.
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Default is 'sgd'.
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- optim_config: A dictionary containing hyperparameters that will be
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passed to the chosen update rule. Each update rule requires different
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hyperparameters (see optim.py) but all update rules require a
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'learning_rate' parameter so that should always be present.
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- lr_decay: A scalar for learning rate decay; after each epoch the
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learning rate is multiplied by this value.
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- batch_size: Size of minibatches used to compute loss and gradient
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during training.
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- num_epochs: The number of epochs to run for during training.
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- print_every: Integer; training losses will be printed every
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print_every iterations.
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- verbose: Boolean; if set to false then no output will be printed
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during training.
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- num_train_samples: Number of training samples used to check training
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accuracy; default is 1000; set to None to use entire training set.
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- num_val_samples: Number of validation samples to use to check val
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accuracy; default is None, which uses the entire validation set.
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- checkpoint_name: If not None, then save model checkpoints here every
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epoch.
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"""
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self.model = model
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self.X_train = data['X_train']
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self.y_train = data['y_train']
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self.X_val = data['X_val']
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self.y_val = data['y_val']
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# Unpack keyword arguments
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self.update_rule = kwargs.pop('update_rule', 'sgd')
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self.optim_config = kwargs.pop('optim_config', {})
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self.lr_decay = kwargs.pop('lr_decay', 1.0)
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self.batch_size = kwargs.pop('batch_size', 100)
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self.num_epochs = kwargs.pop('num_epochs', 10)
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self.num_train_samples = kwargs.pop('num_train_samples', 1000)
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self.num_val_samples = kwargs.pop('num_val_samples', None)
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self.checkpoint_name = kwargs.pop('checkpoint_name', None)
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self.print_every = kwargs.pop('print_every', 10)
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self.verbose = kwargs.pop('verbose', True)
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# Throw an error if there are extra keyword arguments
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if len(kwargs) > 0:
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extra = ', '.join('"%s"' % k for k in list(kwargs.keys()))
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raise ValueError('Unrecognized arguments %s' % extra)
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# Make sure the update rule exists, then replace the string
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# name with the actual function
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if not hasattr(optim, self.update_rule):
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raise ValueError('Invalid update_rule "%s"' % self.update_rule)
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self.update_rule = getattr(optim, self.update_rule)
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self._reset()
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def _reset(self):
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"""
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Set up some book-keeping variables for optimization. Don't call this
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manually.
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"""
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# Set up some variables for book-keeping
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self.epoch = 0
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self.best_val_acc = 0
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self.best_params = {}
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self.loss_history = []
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self.train_acc_history = []
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self.val_acc_history = []
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# Make a deep copy of the optim_config for each parameter
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self.optim_configs = {}
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for p in self.model.params:
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d = {k: v for k, v in self.optim_config.items()}
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self.optim_configs[p] = d
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def _step(self):
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"""
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Make a single gradient update. This is called by train() and should not
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be called manually.
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"""
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# Make a minibatch of training data
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num_train = self.X_train.shape[0]
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batch_mask = np.random.choice(num_train, self.batch_size)
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X_batch = self.X_train[batch_mask]
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y_batch = self.y_train[batch_mask]
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# Compute loss and gradient
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loss, grads = self.model.loss(X_batch, y_batch)
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self.loss_history.append(loss)
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# Perform a parameter update
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for p, w in self.model.params.items():
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dw = grads[p]
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config = self.optim_configs[p]
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next_w, next_config = self.update_rule(w, dw, config)
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self.model.params[p] = next_w
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self.optim_configs[p] = next_config
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def _save_checkpoint(self):
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if self.checkpoint_name is None: return
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checkpoint = {
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'model': self.model,
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'update_rule': self.update_rule,
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'lr_decay': self.lr_decay,
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'optim_config': self.optim_config,
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'batch_size': self.batch_size,
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'num_train_samples': self.num_train_samples,
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'num_val_samples': self.num_val_samples,
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'epoch': self.epoch,
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'loss_history': self.loss_history,
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'train_acc_history': self.train_acc_history,
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'val_acc_history': self.val_acc_history,
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}
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filename = '%s_epoch_%d.pkl' % (self.checkpoint_name, self.epoch)
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if self.verbose:
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print('Saving checkpoint to "%s"' % filename)
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with open(filename, 'wb') as f:
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pickle.dump(checkpoint, f)
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def check_accuracy(self, X, y, num_samples=None, batch_size=100):
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"""
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Check accuracy of the model on the provided data.
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Inputs:
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- X: Array of data, of shape (N, d_1, ..., d_k)
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- y: Array of labels, of shape (N,)
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- num_samples: If not None, subsample the data and only test the model
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on num_samples datapoints.
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- batch_size: Split X and y into batches of this size to avoid using
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too much memory.
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Returns:
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- acc: Scalar giving the fraction of instances that were correctly
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classified by the model.
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"""
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# Maybe subsample the data
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N = X.shape[0]
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if num_samples is not None and N > num_samples:
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mask = np.random.choice(N, num_samples)
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N = num_samples
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X = X[mask]
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y = y[mask]
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# Compute predictions in batches
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num_batches = N // batch_size
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if N % batch_size != 0:
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num_batches += 1
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y_pred = []
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for i in range(num_batches):
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start = i * batch_size
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end = (i + 1) * batch_size
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scores = self.model.loss(X[start:end])
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y_pred.append(np.argmax(scores, axis=1))
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y_pred = np.hstack(y_pred)
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acc = np.mean(y_pred == y)
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return acc
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def train(self):
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"""
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Run optimization to train the model.
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"""
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num_train = self.X_train.shape[0]
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iterations_per_epoch = max(num_train // self.batch_size, 1)
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num_iterations = self.num_epochs * iterations_per_epoch
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for t in range(num_iterations):
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self._step()
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# Maybe print training loss
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if self.verbose and t % self.print_every == 0:
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print('(Iteration %d / %d) loss: %f' % (
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t + 1, num_iterations, self.loss_history[-1]))
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# At the end of every epoch, increment the epoch counter and decay
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# the learning rate.
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epoch_end = (t + 1) % iterations_per_epoch == 0
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if epoch_end:
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self.epoch += 1
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for k in self.optim_configs:
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self.optim_configs[k]['learning_rate'] *= self.lr_decay
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# Check train and val accuracy on the first iteration, the last
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# iteration, and at the end of each epoch.
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first_it = (t == 0)
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last_it = (t == num_iterations - 1)
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if first_it or last_it or epoch_end:
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train_acc = self.check_accuracy(self.X_train, self.y_train,
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num_samples=self.num_train_samples)
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val_acc = self.check_accuracy(self.X_val, self.y_val,
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num_samples=self.num_val_samples)
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self.train_acc_history.append(train_acc)
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self.val_acc_history.append(val_acc)
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self._save_checkpoint()
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if self.verbose:
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print('(Epoch %d / %d) train acc: %f; val_acc: %f' % (
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self.epoch, self.num_epochs, train_acc, val_acc))
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# Keep track of the best model
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if val_acc > self.best_val_acc:
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self.best_val_acc = val_acc
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self.best_params = {}
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for k, v in self.model.params.items():
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self.best_params[k] = v.copy()
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# At the end of training swap the best params into the model
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self.model.params = self.best_params
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