nn.Linear vs torch.matmul

Hi everyone!

I am wondering, why these outputs are different…

my_data = torch.tensor([1,2,3], dtype=torch.float32).repeat(1000, 1)
weights = torch.rand((3,2))
out = torch.matmul(my_data, weights)
print(out)

linear = nn.Linear(3, 2)
output_linear = linear(my_data)
print(output_linear)

out is not close to output_linear…


I would like to recreate following schema and I think my torch.matmul multiplies it correctly… but dont know why nn.Linear gives my different results just…

obv. you have to compare the module with something like matmul(my_data, linear.weights.T) + linear.bias

1 Like

hmmm,

out = torch.matmul(my_data, weights) + 1.
linear = nn.Linear(3, 2)

this way?

this way @Damian_Andrysiak

>>> linear = torch.nn.Linear(3, 3)
>>> inputs = torch.rand(3, 3)
>>> 
>>> linear(inputs)
tensor([[-0.4848,  0.4174, -0.1633],
        [-0.4428,  0.5404, -0.1470],
        [-0.7272,  0.0770,  0.0321]], grad_fn=<AddmmBackward0>)
>>> torch.mm(inputs, linear.weight.T).add(linear.bias)
tensor([[-0.4848,  0.4174, -0.1633],
        [-0.4428,  0.5404, -0.1470],
        [-0.7272,  0.0770,  0.0321]], grad_fn=<AddBackward0>)
>>> 

You were using weights and 1 instead of the layer parameters.

1 Like

ok, works for me. Could you tell me please, does I do it right way? I mean about multiplication weights like on my paint:

       output = torch.matmul(x, self.weights_ih) + self.bias_ih

where:

        self.weights_ih = torch.rand((input_features, input_features), device=device)    
        self.bias_ih = torch.rand((input_features), device=device)