# What function is used when no activation function?

According to tf.keras.layers.Dense  |  TensorFlow v2.13.0, if no activation is applied, it is: a(x) = x. Then why bother to even have this layer with no activation function?

And by calculating the params for the user model, clearly the final layer without activation function has W and b values. So there is some activation function applied?

What function is used when no activation function?

When no activation function is specified, layer output is w^T \cdot X + b

Linear activation is useful when output layer is required to predict regression output in range [-\infty, \infty] (eg: temperature at a desert based on number of hours since midnight).

So when no activation function is specified, Linear activation function is used.(default)

Then how to understand this:

from TensorFlow doc? Isn’t it meaning when no activation function is specified, y=x ?

Activation is applied on top of the affine transformation i.e. w^T \cdot X + b. Think of it as the following pseudocode:

class Dense:
def forward_pass(self, X):
output = w @ X + b
if self.activation is not None:
output = self.do_activation(output)
return output

1 Like

Thank you so much!

So if specify Linear activation function, it’s actually == no activation function?

Yes.

Thanks!