//! Linear layer
//!
//! This layer applies a linear transformation to the incoming data, `y = x@w.t() + b`.
//! The bias is optional. The `forward` method can be used to apply the layer, it supports input
//! with a batch dimension (so of shape `(b_sz, in_c)`) or without (of shape `(in_c,)`), the
//! output has shape `(b_sz, out_c)` and `(out_c,)` respectively.
//!
//! ```rust
//! use candle::{Tensor, Device::Cpu};
//! use candle_nn::Linear;
//! # fn main() -> candle::Result<()> {
//!
//! let w = Tensor::new(&[[1f32, 2.], [3., 4.], [5., 6.]], &Cpu)?;
//! let layer = Linear::new(w, None); // Use no bias.
//! let xs = Tensor::new(&[[10f32, 100.]], &Cpu)?;
//! let ys = layer.forward(&xs)?;
//! assert_eq!(ys.to_vec2::<f32>()?, &[[210.0, 430.0, 650.0]]);
//! # Ok(()) }
//! ```
use candle::Tensor;

#[derive(Debug)]
pub struct Linear {
    weight: Tensor,
    bias: Option<Tensor>,
}

impl Linear {
    pub fn new(weight: Tensor, bias: Option<Tensor>) -> Self {
        Self { weight, bias }
    }

    pub fn forward(&self, x: &Tensor) -> candle::Result<Tensor> {
        let w = match x.dims() {
            &[bsize, _, _] => self.weight.broadcast_left(bsize)?.t()?,
            _ => self.weight.t()?,
        };
        let x = x.matmul(&w)?;
        match &self.bias {
            None => Ok(x),
            Some(bias) => x.broadcast_add(bias),
        }
    }
}