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Applying knowledge learned from one task or domain to improve learning on related tasks
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Advanced techniques for training and fine-tuning transformer-based language models at scale
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Integrating and reasoning across multiple data modalities including text, images, audio, and video
| name | Transfer Learning |
| category | data-science |
| description | Applying knowledge learned from one task or domain to improve learning on related tasks |
I enable models to leverage knowledge learned from one task or domain to improve learning on different but related tasks. By transferring learned features, weights, or representations, I can significantly reduce training time and data requirements for new problems. This is essential when target domain data is scarce or expensive to obtain.
Feature Transfer: Using pretrained representations as fixed features for new tasks.
Fine-Tuning: Adapting pretrained model weights to new tasks with continued training.
Domain Adaptation: Aligning feature distributions between source and target domains.
Domain Confusion: Training to make source and target domains indistinguishable.
Layer Freezing: Keeping early layers fixed while training later layers.
Progressive Fine-Tuning: Gradually unfreezing layers during training.
Feature Extraction: Using pretrained models as fixed feature extractors.
Model Distillation: Transferring knowledge from large to smaller models.
import torch
import torch.nn as nn
import torch.nn.functional as F
class TransferLearningClassifier:
def __init__(self, num_classes, pretrained_model=None, freeze_backbone=True):
if pretrained_model is None:
pretrained_model = torchvision.models.resnet50(pretrained=True)
self.backbone = pretrained_model
if freeze_backbone:
for param in self.backbone.parameters():
param.requires_grad = False
num_features = self.backbone.fc.in_features
self.backbone.fc = nn.Linear(num_features, num_classes)
self.new_layers = nn.ModuleList([self.backbone.fc])
def forward(self, x):
return self.backbone(x)
def freeze_backbone(self):
for param in self.backbone.parameters():
param.requires_grad = False
def unfreeze_backbone(self, unfreeze_ratio=0.3):
total_layers = len(list(self.backbone.parameters()))
unfreeze_start = int(total_layers * (1 - unfreeze_ratio))
for i, param in enumerate(self.backbone.parameters()):
if i >= unfreeze_start:
param.requires_grad = True
def get_trainable_params(self):
trainable = []
frozen = []
for name, param in self.named_parameters():
if param.requires_grad:
trainable.append(name)
else:
frozen.append(name)
return trainable, frozen
import torch
import torch.nn as nn
import torch.nn.functional as F
class DomainAdaptationNetwork(nn.Module):
def __init__(self, backbone_dim=2048, hidden_dim=512):
super().__init__()
self.feature_extractor = nn.Sequential(
nn.Linear(backbone_dim, hidden_dim),
nn.ReLU(),
nn.Dropout(0.5)
)
self.label_classifier = nn.Linear(hidden_dim, 10)
self.domain_classifier = nn.Sequential(
nn.Linear(hidden_dim, hidden_dim),
nn.ReLU(),
nn.Linear(hidden_dim, 2)
)
def forward(self, x, alpha=1.0):
features = self.feature_extractor(x)
class_output = self.label_classifier(features)
reverse_features = GradientReversalLayer.apply(features, alpha)
domain_output = self.domain_classifier(reverse_features)
return class_output, domain_output
class GradientReversalLayer(torch.autograd.Function):
@staticmethod
def forward(ctx, x, lambda_):
ctx.lambda_ = lambda_
return x.view_as(x)
@staticmethod
def backward(ctx, grad_output):
return grad_output.neg() * ctx.lambda_, None
def dann_loss(class_logits, domain_logits, class_labels, domain_labels, alpha=1.0):
class_loss = F.cross_entropy(class_logits, class_labels)
domain_loss = F.cross_entropy(domain_logits, domain_labels)
return class_loss + alpha * domain_loss
import torch
import torch.nn as nn
import torch.nn.functional as F
class MMDLoss(nn.Module):
def __init__(self, kernel_mul=2.0, kernel_num=5):
super().__init__()
self.kernel_mul = kernel_mul
self.kernel_num = kernel_num
def forward(self, source, target):
batch_size = min(source.size(0), target.size(0))
source = source[:batch_size]
target = target[:batch_size]
kernels = self._get_kernels(source, target)
return sum(kernels) / len(kernels)
def _get_kernels(self, source, target):
kernels = []
n = min(len(source), len(target))
for sigma in self._get_sigmas():
kernel_source = self._gaussian_kernel(source, source, sigma)
kernel_target = self._gaussian_kernel(target, target, sigma)
kernel_cross = self._gaussian_kernel(source, target, sigma)
kernel_source = kernel_source[:n, :n]
kernel_target = kernel_target[:n, :n]
kernel_cross = kernel_cross[:n, :n]
loss = kernel_source.mean() + kernel_target.mean() - 2 * kernel_cross.mean()
kernels.append(loss)
return kernels
def _get_sigmas(self):
bandwidths = []
for _ in range(self.kernel_num):
bandwidth = torch.randn(1) * self.kernel_mul + 1.0
bandwidths.append(bandwidth)
return bandwidths
def _gaussian_kernel(self, x, y, sigma):
n, m = len(x), len(y)
x = x.view(n, -1)
y = y.view(m, -1)
x_sq = torch.sum(x ** 2, dim=1).view(-1, 1)
y_sq = torch.sum(y ** 2, dim=1).view(1, -1)
dist_sq = x_sq + y_sq - 2 * x @ y.t()
return torch.exp(-dist_sq / (2 * sigma ** 2))
import torch
import torch.nn as nn
from transformers import AutoModelForSequenceClassification
class BertFineTuner:
def __init__(self, model_name="bert-base-uncased", num_labels=2, learning_rate=2e-5):
self.model = AutoModelForSequenceClassification.from_pretrained(
model_name,
num_labels=num_labels
)
self.learning_rate = learning_rate
def get_optimizer(self):
no_decay = ['bias', 'LayerNorm.weight']
optimizer_grouped_parameters = [
{'params': [p for n, p in self.model.named_parameters()
if not any(nd in n for nd in no_decay)],
'weight_decay': 0.01},
{'params': [p for n, p in self.model.named_parameters()
if any(nd in n for nd in no_decay)],
'weight_decay': 0.0}
]
return torch.optim.AdamW(optimizer_grouped_parameters, lr=self.learning_rate)
def freeze_encoder(self, num_layers_to_freeze=10):
for param in self.model.bert.embeddings.parameters():
param.requires_grad = False
for i in range(num_layers_to_freeze):
for param in self.model.bert.encoder.layer[i].parameters():
param.requires_grad = False
import torch
import torch.nn as nn
import torch.nn.functional as F
class ModelDistillation:
def __init__(self, teacher_model, student_model, temperature=2.0, alpha=0.5):
self.teacher = teacher_model
self.student = student_model
self.temperature = temperature
self.alpha = alpha
def distillation_loss(self, student_logits, teacher_logits, true_labels):
soft_targets = F.softmax(teacher_logits / self.temperature, dim=1)
soft_prob = F.log_softmax(student_logits / self.temperature, dim=1)
soft_loss = F.kl_div(soft_prob, soft_targets, reduction='batchmean') * (self.temperature ** 2)
hard_loss = F.cross_entropy(student_logits, true_labels)
return self.alpha * hard_loss + (1 - self.alpha) * soft_loss
Choose pretrained models that are close to your target domain for better transfer.
Start with frozen backbone and train only new layers before gradually unfreezing.
Use lower learning rates for pretrained layers compared to new random layers.
Apply data augmentation to limited target domain data.
Monitor for negative transfer when source and target domains are too dissimilar.
Use domain adaptation techniques when domain shift is significant.
Consider layer-wise fine-tuning for very different target domains.
Validate on held-out target domain data to detect overfitting.
Use smaller batch sizes and longer training when fine-tuning.
Consider partial fine-tuning (only top layers) for very small datasets.