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diff --git a/tensorflow/g3doc/resources/dims_types.md b/tensorflow/g3doc/resources/dims_types.md new file mode 100644 index 0000000000..eebd80efaa --- /dev/null +++ b/tensorflow/g3doc/resources/dims_types.md @@ -0,0 +1,68 @@ +# Tensor Ranks, Shapes, and Types + +TensorFlow programs use a tensor data structure to represent all data. You can +think of a TensorFlow tensor as an n-dimensional array or list. +A tensor has a static type and dynamic dimensions. Only tensors may be passed +between nodes in the computation graph. + +## Rank + +In the TensorFlow system, tensors are described by a unit of dimensionality +known as *rank*. Tensor rank is not the same as matrix rank. Tensor rank +(sometimes referred to as *order* or *degree* or *n-dimension*) is the number +of dimensions of the tensor. For example, the following tensor (defined as a +Python list) has a rank of 2: + + t = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] + +A rank two tensor is what we typically think of as a matrix, a rank on tensor +is a vector. For a rank two tensor you can acccess any element with the syntax +`t[i, j]`. For a rank three tensor you would need to address an element with +'t[i, j, k]'. + +Rank | Math entity | Python example +--- | --- | --- +0 | Scalar (magnitude only) | `s = 483` +1 | Vector (magnitude and direction) | `v = [1.1, 2.2, 3.3]` +2 | Matrix (table of numbers) | `m = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]` +3 | 3-Tensor (cube of numbers] | `t = [[[2], [4], [6]], [[8], [10], [12]], [[14], [16], [18]]]` +n | n-Tensor (you get the idea) | `....` + +## Shape + +The TensorFlow documentation uses three notational conventions to describe +tensor dimensionality: rank, shape, and dimension number. The following table +shows how these relate to one another: + +Rank | Shape | Dimension number | Example +--- | --- | --- | --- +0 | [] | 0-D | A 0-D tensor. A scalar. +1 | [D0] | 1-D | A 1-D tensor with shape [5]. +2 | [D0, D1] | 2-D | A 2-D tensor with shape [3, 4]. +3 | [D0, D1, D2] | 3-D | A 3-D tensor with shape [1, 4, 3]. +n | [D0, D1, ... Dn] | n-D | A tensor with shape [D0, D1, ... Dn]. + +Shapes can be represented via Python lists / tuples of ints, or with the +[`TensorShape` class](../api_docs/python/framework.md#TensorShape). + +## Data types + +In addition to dimensionality, Tensors have a data type. You can assign any one +of the following data types to a tensor: + +Data type | Python type | Description +--- | --- | --- +`DT_FLOAT` | `tf.float32` | 32 bits floating point. +`DT_DOUBLE` | `tf.float64` | 64 bits floating point. +`DT_INT64` | `tf.int64` | 64 bits signed integer. +`DT_INT32` | `tf.int32` | 32 bits signed integer. +`DT_INT16` | `tf.int16` | 16 bits signed integer. +`DT_INT8` | `tf.int8` | 8 bits signed integer. +`DT_UINT8` | `tf.uint8` | 8 bits unsigned integer. +`DT_STRING` | `tf.string` | Variable length byte arrays. Each element of a Tensor is a byte array. +`DT_BOOL` | `tf.bool` | Boolean. +`DT_COMPLEX64` | `tf.complex64` | Complex number made of two 32 bits floating points: real and imaginary parts. +`DT_QINT32` | `tf.qint32` | 32 bits signed integer used in quantized Ops. +`DT_QINT8` | `tf.qint8` | 8 bits signed integer used in quantized Ops. +`DT_QUINT8` | `tf.quint8` | 8 bits unsigned integer used in quantized Ops. + |