MullOverThing

Useful tips for everyday

# Why we need sigmoid activation function What are the major drawbacks of it?

## Why we need sigmoid activation function What are the major drawbacks of it?

However, sigmoid activation functions have become less popular over the period of time due to the following two major drawbacks: Killing gradients: Sigmoid neurons get saturated on the boundaries and hence the local gradients at these regions is almost zero. Hence, effectively making the local gradient to near 0.

Why is sigmoid not good?

Disadvantage: Sigmoid: tend to vanish gradient (cause there is a mechanism to reduce the gradient as “a” increase, where “a” is the input of a sigmoid function. Gradient of Sigmoid: S′(a)=S(a)(1−S(a)). When “a” grows to infinite large , S′(a)=S(a)(1−S(a))=1×(1−1)=0).

What are the problems with using a sigmoid activation function?

The two major problems with sigmoid activation functions are: Sigmoid saturate and kill gradients: The output of sigmoid saturates (i.e. the curve becomes parallel to x-axis) for a large positive or large negative number. Thus, the gradient at these regions is almost zero.

### What is the use of sigmoid function?

The main reason why we use sigmoid function is because it exists between (0 to 1). Therefore, it is especially used for models where we have to predict the probability as an output. Since probability of anything exists only between the range of 0 and 1, sigmoid is the right choice.

By Nishant Nikhil, IIT Kharagpur Recently I and Rajasekhar (for a KWoC project) were analyzing how different activation functions interact among themselves, and we found that using relu after sigmoid in the last two layers worsens the performance of the model.

What is the problem with sigmoid during backpropagation?

The sigmoid activation function This causes vanishing gradients and poor learning for deep networks. This can occur when the weights of our networks are initialized poorly – with too-large negative and positive values.

#### What is the difference between Softmax and sigmoid?

Softmax is used for multi-classification in the Logistic Regression model, whereas Sigmoid is used for binary classification in the Logistic Regression model. This is how the Softmax function looks like this: This is similar to the Sigmoid function. This is main reason why the Softmax is cool.

Is ReLU a loss function?

ReLU is a famous, widely-used non-linear activation function, which stands for Rectified Linear Unit (goes along the lines of “if x≤0, y=0 else y=1”). Thus, it’s only activated when the values are positive. ReLU is considered a go-to function if one is new to activation function or is unsure about which one to choose.

Is ReLU a continuous function?

To address this question, let us look at the mathematical definition of the ReLU function: or expressed as a piece-wise defined function: Since f(0)=0 for both the top and bottom part of the previous equation, the ReLU function, we can clearly see that the function is continuous.

## Which is the form of the sigmoid activation function?

The sigmoid activation function has the mathematical form `sig (z) = 1/ (1 + e^-z)`. As we can see, it basically takes a real valued number as the input and squashes it between 0 and 1. It is often termed as a squashing function as well.

Why do we need the non-linearity of activation functions?

The non-linearity is where we get the wiggle and the network learns to capture complicated relationships. As we can see from the above mathematical representation, a large negative number passed through the sigmoid function becomes 0 and a large positive number becomes 1.

Why do we need activation functions in neurons?

However, there are concepts such as Leaky ReLU that can be used to overcome this problem. Also, having a proper setting of the learning rate can prevent causing the neurons to be dead. The Leaky ReLU is just an extension of the traditional ReLU function.