# diag¶

`paddle.` `diag` ( x, offset=0, padding_value=0, name=None ) [source]

If `x` is a vector (1-D tensor), a 2-D square tensor whth the elements of `x` as the diagonal is returned.

If `x` is a matrix (2-D tensor), a 1-D tensor with the diagonal elements of `x` is returned.

The argument `offset` controls the diagonal offset:

If `offset` = 0, it is the main diagonal.

If `offset` > 0, it is superdiagonal.

If `offset` < 0, it is subdiagonal.

Parameters
• x (Tensor) – The input tensor. Its shape is either 1-D or 2-D. Its data type should be float32, float64, int32, int64.

• offset (int, optional) – The diagonal offset. A positive value represents superdiagonal, 0 represents the main diagonal, and a negative value represents subdiagonal.

• padding_value (int|float, optional) – Use this value to fill the area outside the specified diagonal band. Only takes effect when the input is a 1-D Tensor. The default value is 0.

• name (str, optional) – Name for the operation (optional, default is None). For more information, please refer to Name.

Returns

Tensor, a square matrix or a vector. The output data type is the same as input data type.

Examples

```import paddle

paddle.disable_static()
x = paddle.to_tensor([1, 2, 3])
y = paddle.diag(x)
print(y.numpy())
# [[1 0 0]
#  [0 2 0]
#  [0 0 3]]

y = paddle.diag(x, offset=1)
print(y.numpy())
# [[0 1 0 0]
#  [0 0 2 0]
#  [0 0 0 3]
#  [0 0 0 0]]

y = paddle.diag(x, padding_value=6)
print(y.numpy())
# [[1 6 6]
#  [6 2 6]
#  [6 6 3]]
```
```import paddle

paddle.disable_static()
x = paddle.to_tensor([[1, 2, 3], [4, 5, 6]])
y = paddle.diag(x)
print(y.numpy())
# [1 5]

y = paddle.diag(x, offset=1)
print(y.numpy())
# [2 6]

y = paddle.diag(x, offset=-1)
print(y.numpy())
# 
```