library(torch)

# creates example tensors. x requires_grad = TRUE tells that 
# we are going to take derivatives over it.
dense <- nn_module(
  clasname = "dense",
  # the initialize function tuns whenever we instantiate the model
  initialize = function(in_features, out_features) {
    
    # just for you to see when this function is called
    cat("Calling initialize!") 
    
    # we use nn_parameter to indicate that those tensors are special
    # and should be treated as parameters by `nn_module`.
    self$w <- nn_parameter(torch_randn(in_features, out_features))
    self$b <- nn_parameter(torch_zeros(out_features))
    
  },
  # this function is called whenever we call our model on input.
  forward = function(x) {
    cat("Calling forward!")
    torch_mm(x, self$w) + self$b
  }
)

model <- dense(3, 1)
## Calling initialize!
# you can get all parameters 
model$parameters
## $w
## torch_tensor
##  2.6829
## -0.4501
##  1.8055
## [ CPUFloatType{3,1} ]
## 
## $b
## torch_tensor
##  0
## [ CPUFloatType{1} ]
# or individually
model$w
## torch_tensor
##  2.6829
## -0.4501
##  1.8055
## [ CPUFloatType{3,1} ]
model$b
## torch_tensor
##  0
## [ CPUFloatType{1} ]
# create an input tensor
x <- torch_randn(10, 3)
y_pred <- model(x)
## Calling forward!
y_pred
## torch_tensor
## -3.2543
## -4.0736
## -0.4706
## -2.5269
##  3.6924
##  5.9955
## -3.4914
##  0.9271
##  1.3105
##  2.7783
## [ CPUFloatType{10,1} ]