Tensor Attributes — PyTorch 2.0 documentation (original) (raw)

Each torch.Tensor has a torch.dtype, torch.device, and torch.layout.

torch.dtype¶

class torch.dtype¶

A torch.dtype is an object that represents the data type of atorch.Tensor. PyTorch has twelve different data types:

To find out if a torch.dtype is a floating point data type, the property is_floating_pointcan be used, which returns True if the data type is a floating point data type.

To find out if a torch.dtype is a complex data type, the property is_complexcan be used, which returns True if the data type is a complex data type.

When the dtypes of inputs to an arithmetic operation (add, sub, div, mul) differ, we promote by finding the minimum dtype that satisfies the following rules:

• If the type of a scalar operand is of a higher category than tensor operands (where complex > floating > integral > boolean), we promote to a type with sufficient size to hold all scalar operands of that category.
• If a zero-dimension tensor operand has a higher category than dimensioned operands, we promote to a type with sufficient size and category to hold all zero-dim tensor operands of that category.
• If there are no higher-category zero-dim operands, we promote to a type with sufficient size and category to hold all dimensioned operands.

A floating point scalar operand has dtype torch.get_default_dtype() and an integral non-boolean scalar operand has dtype torch.int64. Unlike numpy, we do not inspect values when determining the minimum dtypes of an operand. Quantized and complex types are not yet supported.

Promotion Examples:

float_tensor = torch.ones(1, dtype=torch.float) double_tensor = torch.ones(1, dtype=torch.double) complex_float_tensor = torch.ones(1, dtype=torch.complex64) complex_double_tensor = torch.ones(1, dtype=torch.complex128) int_tensor = torch.ones(1, dtype=torch.int) long_tensor = torch.ones(1, dtype=torch.long) uint_tensor = torch.ones(1, dtype=torch.uint8) double_tensor = torch.ones(1, dtype=torch.double) bool_tensor = torch.ones(1, dtype=torch.bool)

zero-dim tensors

long_zerodim = torch.tensor(1, dtype=torch.long) int_zerodim = torch.tensor(1, dtype=torch.int)

torch.add(5, 5).dtype torch.int64

5 is an int64, but does not have higher category than int_tensor so is not considered.

(int_tensor + 5).dtype torch.int32 (int_tensor + long_zerodim).dtype torch.int32 (long_tensor + int_tensor).dtype torch.int64 (bool_tensor + long_tensor).dtype torch.int64 (bool_tensor + uint_tensor).dtype torch.uint8 (float_tensor + double_tensor).dtype torch.float64 (complex_float_tensor + complex_double_tensor).dtype torch.complex128 (bool_tensor + int_tensor).dtype torch.int32

Since long is a different kind than float, result dtype only needs to be large enough

to hold the float.

torch.add(long_tensor, float_tensor).dtype torch.float32

When the output tensor of an arithmetic operation is specified, we allow casting to its dtype except that:

• An integral output tensor cannot accept a floating point tensor.
• A boolean output tensor cannot accept a non-boolean tensor.
• A non-complex output tensor cannot accept a complex tensor

Casting Examples:

allowed:

float_tensor *= float_tensor float_tensor *= int_tensor float_tensor *= uint_tensor float_tensor *= bool_tensor float_tensor *= double_tensor int_tensor *= long_tensor int_tensor *= uint_tensor uint_tensor *= int_tensor

disallowed (RuntimeError: result type can't be cast to the desired output type):

int_tensor *= float_tensor bool_tensor *= int_tensor bool_tensor *= uint_tensor float_tensor *= complex_float_tensor

torch.device¶

class torch.device¶

A torch.device is an object representing the device on which a torch.Tensor is or will be allocated.

The torch.device contains a device type ('cpu', 'cuda' or 'mps') and optional device ordinal for the device type. If the device ordinal is not present, this object will always represent the current device for the device type, even after torch.cuda.set_device() is called; e.g., a torch.Tensor constructed with device 'cuda' is equivalent to 'cuda:X' where X is the result of torch.cuda.current_device().

A torch.Tensor’s device can be accessed via the Tensor.device property.

A torch.device can be constructed via a string or via a string and device ordinal

Via a string:

torch.device('cuda:0') device(type='cuda', index=0)

torch.device('cpu') device(type='cpu')

torch.device('mps') device(type='mps')

torch.device('cuda') # current cuda device device(type='cuda')

Via a string and device ordinal:

torch.device('cuda', 0) device(type='cuda', index=0)

torch.device('mps', 0) device(type='mps', index=0)

torch.device('cpu', 0) device(type='cpu', index=0)

The device object can also be used as a context manager to change the default device tensors are allocated on:

with torch.device('cuda:1'): ... r = torch.randn(2, 3) r.device device(type='cuda', index=1)

This context manager has no effect if a factory function is passed an explicit, non-None device argument. To globally change the default device, see alsotorch.set_default_device().

Note

The torch.device argument in functions can generally be substituted with a string. This allows for fast prototyping of code.

Example of a function that takes in a torch.device

cuda1 = torch.device('cuda:1') torch.randn((2,3), device=cuda1)

You can substitute the torch.device with a string

torch.randn((2,3), device='cuda:1')

Note

For legacy reasons, a device can be constructed via a single device ordinal, which is treated as a cuda device. This matches Tensor.get_device(), which returns an ordinal for cuda tensors and is not supported for cpu tensors.

torch.device(1) device(type='cuda', index=1)

Note

Methods which take a device will generally accept a (properly formatted) string or (legacy) integer device ordinal, i.e. the following are all equivalent:

torch.randn((2,3), device=torch.device('cuda:1')) torch.randn((2,3), device='cuda:1') torch.randn((2,3), device=1) # legacy

torch.layout¶

class torch.layout¶

Warning

The torch.layout class is in beta and subject to change.

A torch.layout is an object that represents the memory layout of atorch.Tensor. Currently, we support torch.strided (dense Tensors) and have beta support for torch.sparse_coo (sparse COO Tensors).

torch.strided represents dense Tensors and is the memory layout that is most commonly used. Each strided tensor has an associatedtorch.Storage, which holds its data. These tensors provide multi-dimensional, stridedview of a storage. Strides are a list of integers: the k-th stride represents the jump in the memory necessary to go from one element to the next one in the k-th dimension of the Tensor. This concept makes it possible to perform many tensor operations efficiently.

Example:

x = torch.tensor([[1, 2, 3, 4, 5], [6, 7, 8, 9, 10]]) x.stride() (5, 1)

x.t().stride() (1, 5)

For more information on torch.sparse_coo tensors, see torch.sparse.

torch.memory_format¶

class torch.memory_format¶

A torch.memory_format is an object representing the memory format on which a torch.Tensor is or will be allocated.

Possible values are:

• torch.contiguous_format: Tensor is or will be allocated in dense non-overlapping memory. Strides represented by values in decreasing order.
• torch.channels_last: Tensor is or will be allocated in dense non-overlapping memory. Strides represented by values instrides[0] > strides[2] > strides[3] > strides[1] == 1 aka NHWC order.
• torch.channels_last_3d: Tensor is or will be allocated in dense non-overlapping memory. Strides represented by values instrides[0] > strides[2] > strides[3] > strides[4] > strides[1] == 1 aka NDHWC order.
• torch.preserve_format: Used in functions like clone to preserve the memory format of the input tensor. If input tensor is allocated in dense non-overlapping memory, the output tensor strides will be copied from the input. Otherwise output strides will follow torch.contiguous_format