@ptrblck, you are right about the input shape correspondece to [batch_size = 6, seq_len = 3, channels = 1]! @Nikronic, yes I only have 6 samples. I permuted the input so to get one of dimensions (6,1,3) = [batch_size, channels, seq_len]. Yes, I was missing another nn.ReLU() after the Conv1d layer.
I modified MyNet as following:
f = nn.Sequential(
        nn.Conv1d(1,64,2),
        nn.ReLU(),
        nn.MaxPool1d(2),
        nn.Flatten(start_dim=1),
        nn.Linear(64,50),
        nn.ReLU(),
        nn.Linear(50, 1)
        )

again, it does not work. I get the following error: Given groups=1, weight of size [64, 1, 2], expected input[6, 6, 3] to have 1 channels, but got 6 channels instead
Please, Can you give me any clue about what it’s wrong?