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Introduction || Quick Start || Tensor || Dataset || Transforms || Model || Autograd || Train || Save and load

Quick Start

This section quickly implements a simple deep learning model through MindSpore APIs. For a deeper understanding of how to use MindSpore, see the reference links provided at the end of each section.

import mindspore
from mindspore import nn
from mindspore import ops
from mindspore.dataset import vision, transforms
from mindspore.dataset import MnistDataset

Processing a Dataset

MindSpore provides Pipeline-based Data Engine and achieves efficient data preprocessing through Dataset and Transforms. In this tutorial, we use the Mnist dataset and pre-process dataset by using the data transformations provided by mindspore.dataset, after automatically downloaded.

The sample code in this chapter relies on download, which can be installed by using the command pip install download. If this document is run as Notebook, you need to restart the kernel after installation to execute subsequent code.

# Download data from open datasets\n",
from download import download

url = "https://mindspore-website.obs.cn-north-4.myhuaweicloud.com/" \
      "notebook/datasets/MNIST_Data.zip"
path = download(url, "./", kind="zip", replace=True)

Downloading data from https://mindspore-website.obs.cn-north-4.myhuaweicloud.com/notebook/datasets/MNIST_Data.zip (10.3 MB)

file_sizes: 100%|██████████████████████████| 10.8M/10.8M [00:01<00:00, 6.73MB/s]
Extracting zip file...
Successfully downloaded / unzipped to ./

After the data is downloaded, the dataset object is obtained.

train_dataset = MnistDataset('MNIST_Data/train')
test_dataset = MnistDataset('MNIST_Data/test')

Print the names of the data columns contained in the dataset for dataset pre-processing.

print(train_dataset.get_col_names())

['image', 'label']

Dataset in MindSpore uses the Data Processing Pipeline, which requires specifying operations such as map, batch, and shuffle. Here we use map to transform the image data and the label, and then pack the processed dataset into a batch of size 64.

def datapipe(dataset, batch_size):
    image_transforms = [
        vision.Rescale(1.0 / 255.0, 0),
        vision.Normalize(mean=(0.1307,), std=(0.3081,)),
        vision.HWC2CHW()

    label_transform = transforms.TypeCast(mindspore.int32)

    dataset = dataset.map(image_transforms, 'image')
    dataset = dataset.map(label_transform, 'label')
    dataset = dataset.batch(batch_size)
    return dataset

train_dataset = datapipe(train_dataset, 64)
test_dataset = datapipe(test_dataset, 64)

Use create_tuple_iterator or create_dict_iterator to iterate over the dataset.

for image, label in test_dataset.create_tuple_iterator():
    print(f"Shape of image [N, C, H, W]: {image.shape} {image.dtype}")
    print(f"Shape of label: {label.shape} {label.dtype}")
    break

Shape of image [N, C, H, W]: (64, 1, 28, 28) Float32
Shape of label: (64,) Int32

for data in test_dataset.create_dict_iterator():
    print(f"Shape of image [N, C, H, W]: {data['image'].shape} {data['image'].dtype}")
    print(f"Shape of label: {data['label'].shape} {data['label'].dtype}")
    break

Shape of image [N, C, H, W]: (64, 1, 28, 28) Float32
Shape of label: (64,) Int32

For more detailed information, see Dataset and Transforms.

Building Network

mindspore.nn class is the base class for building all networks and is the basic unit of the network. When the user needs to customize the network, you can inherit the nn.Cell class and override the __init__ method and the construct method. __init__ contains the definitions of all network layers, and construct contains the transformation process of the data (Tensor) (i.e. the construction process of the computational graph).

# Define model
class Network(nn.Cell):
    def __init__(self):
        super().__init__()
        self.flatten = nn.Flatten()
        self.dense_relu_sequential = nn.SequentialCell(
            nn.Dense(28*28, 512),
            nn.ReLU(),
            nn.Dense(512, 512),
            nn.ReLU(),
            nn.Dense(512, 10)
        )

    def construct(self, x):
        x = self.flatten(x)
        logits = self.dense_relu_sequential(x)
        return logits

model = Network()
print(model)

Network<
  (flatten): Flatten<>
  (dense_relu_sequential): SequentialCell<
    (0): Dense<input_channels=784, output_channels=512, has_bias=True>
    (1): ReLU<>
    (2): Dense<input_channels=512, output_channels=512, has_bias=True>
    (3): ReLU<>
    (4): Dense<input_channels=512, output_channels=10, has_bias=True>
    >
  >

For more detailed information, see Model.

Training Model

# Instantiate loss function and optimizer
loss_fn = nn.CrossEntropyLoss()
optimizer = nn.SGD(model.trainable_params(), 1e-2)

In model training, a complete training process (step) requires the following three steps:

  1. Forward calculation: model predicts results (logits) and finds the prediction loss (loss) with the correct label (label).

  2. Backpropagation: Using an automatic differentiation mechanism, the gradients of the model parameters (parameters) with respect to the loss are automatically found.

  3. Parameter optimization: update the gradient to the parameter.

MindSpore uses a functional automatic differentiation mechanism, implemented through the steps above:

  1. Define forward calculation function.

  2. Obtain the gradient calculation function by function transformation.

  3. Define training functions, and perform forward computation, back propagation and parameter optimization.

def train(model, dataset, loss_fn, optimizer):
    # Define forward function
    def forward_fn(data, label):
        logits = model(data)
        loss = loss_fn(logits, label)
        return loss, logits

    # Get gradient function
    grad_fn = ops.value_and_grad(forward_fn, None, optimizer.parameters, has_aux=True)

    # Define function of one-step training
    def train_step(data, label):
        (loss, _), grads = grad_fn(data, label)
        loss = ops.depend(loss, optimizer(grads))
        return loss

    size = dataset.get_dataset_size()
    model.set_train()
    for batch, (data, label) in enumerate(dataset.create_tuple_iterator()):
        loss = train_step(data, label)

        if batch % 100 == 0:
            loss, current = loss.asnumpy(), batch
            print(f"loss: {loss:>7f}  [{current:>3d}/{size:>3d}]")

In addition to training, we define test functions that are used to evaluate the performance of the model.

def test(model, dataset, loss_fn):
    num_batches = dataset.get_dataset_size()
    model.set_train(False)
    total, test_loss, correct = 0, 0, 0
    for data, label in dataset.create_tuple_iterator():
        pred = model(data)
        total += len(data)
        test_loss += loss_fn(pred, label).asnumpy()
        correct += (pred.argmax(1) == label).asnumpy().sum()
    test_loss /= num_batches
    correct /= total
    print(f"Test: \n Accuracy: {(100*correct):>0.1f}%, Avg loss: {test_loss:>8f} \n")

The training process requires several iterations of the dataset, and one complete iteration is called an epoch. In each round, the training set is traversed for training and the test set is used for prediction at the end. The loss value and prediction accuracy (Accuracy) of each round are printed, and it can be seen that the loss is decreasing and Accuracy is increasing.

epochs = 3
for t in range(epochs):
    print(f"Epoch {t+1}\n-------------------------------")
    train(model, train_dataset, loss_fn, optimizer)
    test(model, test_dataset, loss_fn)
print("Done!")

Epoch 1
-------------------------------
loss: 2.302088  [  0/938]
loss: 2.290692  [100/938]
loss: 2.266338  [200/938]
loss: 2.205240  [300/938]
loss: 1.907198  [400/938]
loss: 1.455603  [500/938]
loss: 0.861103  [600/938]
loss: 0.767219  [700/938]
loss: 0.422253  [800/938]
loss: 0.513922  [900/938]
Test:
 Accuracy: 83.8%, Avg loss: 0.529534

Epoch 2
-------------------------------
loss: 0.580867  [  0/938]
loss: 0.479347  [100/938]
loss: 0.677991  [200/938]
loss: 0.550141  [300/938]
loss: 0.226565  [400/938]
loss: 0.314738  [500/938]
loss: 0.298739  [600/938]
loss: 0.459540  [700/938]
loss: 0.332978  [800/938]
loss: 0.406709  [900/938]
Test:
 Accuracy: 90.2%, Avg loss: 0.334828

Epoch 3
-------------------------------
loss: 0.461890  [  0/938]
loss: 0.242303  [100/938]
loss: 0.281414  [200/938]
loss: 0.207835  [300/938]
loss: 0.206000  [400/938]
loss: 0.409646  [500/938]
loss: 0.193608  [600/938]
loss: 0.217575  [700/938]
loss: 0.212817  [800/938]
loss: 0.202862  [900/938]
Test:
 Accuracy: 91.9%, Avg loss: 0.280962

Done!

For the detailed information, see Train.

Saving a Model

After the model is trained, its parameters need to be saved.

# Save checkpoint
mindspore.save_checkpoint(model, "model.ckpt")
print("Saved Model to model.ckpt")

Saved Model to model.ckpt

Loading a Model

There are two steps to load the saved weights:

  1. Reinstantiate the model object and construct the model.

  2. Load the model parameters and load them onto the model.

# Instantiate a random initialized model
model = Network()
# Load checkpoint and load parameter to model
param_dict = mindspore.load_checkpoint("model.ckpt")
param_not_load = mindspore.load_param_into_net(model, param_dict)
print(param_not_load)

[]

param_not_load is an unloaded parameter list. When the list is empty, it means all parameters are loaded successfully.

The loaded model can be used directly for predictive inference.

model.set_train(False)
for data, label in test_dataset:
    pred = model(data)
    predicted = pred.argmax(1)
    print(f'Predicted: "{predicted[:10]}", Actual: "{label[:10]}"')
    break

Predicted: "Tensor(shape=[10], dtype=Int32, value= [3, 9, 6, 1, 6, 7, 4, 5, 2, 2])", Actual: "Tensor(shape=[10], dtype=Int32, value= [3, 9, 6, 1, 6, 7, 4, 5, 2, 2])"

For more detailed information, see Save and Load.