# tensorplay.nn.attention.bias.causal_upper_left

Source: https://www.tensorplay.cn/docs/generated/tensorplay.nn.attention.bias.causal_upper_left.html

```python
tensorplay.nn.attention.bias.causal_upper_left(*size) → CausalBias
```

Creates an upper-left triangular causal bias.

This function generates an upper-left triangular matrix to represent causal attention bias with a
diagonal offset set so that the inclusive values are aligned to the upper left corner of the matrix.
This equivalent to the is_causal=True argument in scaled_dot_product_attention.

The equivalent code for constructing this bias is:

```
tensorplay.tril(tensorplay.ones(size, dtype=tensorplay.bool))
```

For instance, with shape=(3,4), the materialized bias tensor will be:

```
[[1, 0, 0, 0],
 [1, 1, 0, 0],
 [1, 1, 1, 0]]
```

Parameters:

size – The size of the bias matrix.

Returns:

The UPPER_LEFT triangular causal bias variant.

Return type:

[CausalBias](/docs/generated/tensorplay.nn.attention.bias.CausalBias.html#tensorplay.nn.attention.bias.CausalBias)