Anatomy of Loss Functions: Questions and Answers

Anatomy of Loss Functions: Questions and Answers

A lost function is essential in the evaluation and prediction of the performance of a model. It determines the errors of a model, minimizes found errors, and improves a model’s algorithms. 

In this article, we cover the anatomy (and even the physiology) of loss functions. Providing answers to frequently asked questions, we dissect the flesh and bones of loss functions and present a comprehensive understanding of the term in its skeletal form. 

Understanding Loss Functions in Machine Learning

At its fundamental premise, a loss function is very simple. It’s simply the evaluation of models against a set of datasets. It’s essential to model accuracy and ML governance. To better illustrate this point, we will look at what a loss function means, its types, and uses.

What is a loss function in Machine Learning?

A loss function in Machine Learning shows the disparity between the estimated value of a model’s iteration and its actual value. This disparity can be an estimation of an algorithm’s current output measured against its expected output. Also, it can be an evaluation of how an algorithm prototypes data that make up a model. Whatever form a loss function takes, it remains a practical premise.

Being practical means a loss function is not based on an assumption or opinion. However, serving as a theoretical tool or measure, it examines the decision process of ML problems and reveals their impacts on results. Building an accurate predictor in Deep and Machine Learning requires constant iterations. A loss function reflects if iterations meet the chosen model’s approach and testing. 

A machine learns through a loss function. If the deviation between current values and expected values is too great, the machine responds by exhibiting large numbers which could lead to immense errors in prediction. With the help of optimization functions, however, a loss function is trained to reduce errors in prediction.

How many types of loss functions are there?

Depending on the learning task you’re working on, there are two types of loss functions. A loss function can be part of regression losses or classification losses. Below is a detailed explanation of these two loss functions. 

What is regression loss?

Regression loss involves the prediction of real-valued, continuous quantities. It deals with modeling a linear relationship between a dependent variable and several independent variables. The most used regression neural network loss function is the Mean-Squared Error (MSE).

What is classification loss?

Classification loss involves the prediction of discrete class and label outputs. The difference between regression loss and classification loss is that while regression loss is about predicting quantities, classification loss predicts classes and labels. The most used classification loss is the Binary Cross-Entropy Loss (BCEL).

What is the use of loss function in ML?

The uses of a loss function are its benefits. In ML, loss functions play a significant role in the accuracy of a model. Imagine you’re at the top of a mountain, trying to find out which path to take going down. If you have no idea, you choose anyone and face the consequences. In ML, however, you can use a neural network loss function to predict the best possible path. Generally, loss functions:

  1. Measure how good your prediction model has become.
  2. Predict expected outcomes against actual outcomes.
  3. Optimize the algorithms of your model.
  4. Minimize losses and errors by improving accuracy.
  5. Define the objective performance of your model.
  6. Estimate your parameters and ensure optimality.

What are the commonly-used loss functions?

Loss functions butter modern Machine Learning and this is due to their many benefits. They are especially useful in the understanding of model accuracy and ML governance. There are several lost functions in DL and ML. However, it gets confusing and complex if you do not remember the end goals of each loss function Machine Learning. Below are some of the most commonly used loss functions in Machine Learning.

What is Mean-Squared Error (MSE)?

The Mean-Squared Error shows results for the average squared errors between the estimated value and the actual value. It’s computed by squaring errors to find the average. Due to its straightforward calculation, MSE is regarded as the simplest and most common loss function used in Deep and Machine Learning.

A good Mean-Squared Value (MSE) is subjective, meaning there is no general agreement on what a good MSE should be. But the lower the MSE, the better the prediction and, therefore, the greater the model accuracy. A zero MSE suggests a perfect model. A 100% MSE reflects a great correlation between a model’s accuracy and its training time. 

What is Cross-Entropy Loss (CEL)?

Cross-entropy Loss measures how a classification model performs when the probability value is between 0 and 1. It shows the variation between two probability distributions and the relative entropy between them. Also known as log loss or algorithmic loss, it works as an evaluation metric and penalizes false classifiers for improved accuracy.

What is Huber Loss?

Huber Loss combines properties from Mean Absolute Error (MAE) and Mean-Squared Error (MSE). Although it’s less sensitive to data outliers than MSE, Huber Loss allows you to penalize outliers more easily for greater accuracy. Huber Loss is said to be robust against outliers due to how errors and corresponding distribution coincide with the heavy-tailed Laplace distribution. 

What is Hinge Loss?

Hinge Loss trains data classifiers especially in Support Vector Machines (SVM). If there’s a negative distance from the classification boundary, it means the boundary is wrong and the classifier would be incorrectly justified. The difference between Log Loss and Hinge Loss is in the estimation of probabilities. While the former provides accuracy in estimating probabilities, the latter provides sparsity and accuracy.

Loss functions Vs Other Functions: Difference, Features, and Similarities

There are several functions that compare greatly with loss functions. To dissect what loss functions are, it is pertinent we look at these other functions. Read through the different types of functions there are and the differences, features, and similarities between these functions and loss functions.

What is the difference between loss function and error function?

A loss function might appear similar to an error function, but it’s not. Whereas a loss function works on an error to quantify its negative results, an error function measures the deviation of a value from its prediction. However, a loss function can be likened to an error function through how both are used for a single training model. 

Training loss in ML implies deriving value from an objective function you’re minimizing. The value could be positive or negative, depending on the objective for training your data. On the other hand, training error indicates the percentage of training examples your model gets wrong. By using error rate, it shows the performance of your model.

What is the difference between loss function and activation function?

A loss function determines your whole model, predicts its performance, and improves its accuracy. It does this by calculating the error for every data training. An activation function is different as it’s a property of a neuron and not exactly the overall goal of your model. Nevertheless, an activation function contributes towards the success of a loss function.

Another way to look at the difference between a loss function and an activation function is through the optimal gradient of loss functions and coefficients. While a loss function minimizes errors to find the most optimal gradients, an activation function gets activated to help in achieving the gradients.

What is the difference between loss function and cost function?

Loss functions mostly apply to a single training set and are achieved by minimizing errors. Cost functions apply to multiple training sets rather than a single one. They work by minimization and maximization. If cost functions are minimized, it means the returned values for the model’s parameters are large. If cost functions are maximized, it means the returned values are small.

In the battle of cost function vs loss function, there’s no winner. When calculating cost functions, we look for the average of loss functions. That way, we can say the loss function is an integral part of the cost function. The difference is in the calculation. While a loss function calculates values at every instance, a cost function computes values only once. 

What is the difference between loss function and objective function?

An objective function is a function specified for either minimization or maximization. It’s an optimization term that embodies the set of functions we’re optimizing and the constraints involved in achieving the optimization. A loss function only tells the prediction of a model and its performance, based on the computation of errors.

The catch is that an objective function is a function we want to either minimize or maximize. At the stage of minimizing or maximizing that function, it becomes a cost function, a loss function, or an error function. Therefore, every loss function must have been stated as an objective function.

What is the difference between loss function and optimizer?

Is optimizer the same as loss function? No, it’s not. An exponential loss function shows the difference between the actual and the expected, reducing weights and biases. These weights are modified by an optimizer or optimization function. So, whenever a loss function determines an error to improve a model, an optimizer shapes the model by adjusting the weights.

In other words, a loss function calculates losses while an optimizer overcomes losses. Using gradients, we can see that if a loss function were a car rolling into a deep pit, an optimizer would be its break and tires due to how it shapes and modifies the direction of a loss function. In a nutshell, both functions are needed for a greater model prediction and an effective performance of model computation.

Training and interpreting loss functions in Machine Learning

Loss functions in Deep Learning are trained on datasets. But how does this training work and how do we predict? Below, we answer questions related to training and interpreting loss functions in Machine Learning. Read on to see what it means.

What is training loss in neural networks?

Training loss in neural networks is the error per epoch on the training set of data. As a model’s epoch increases, the training loss drops. If the training loss is zero, we say the model’s prediction is perfect and correlates with training time. Therefore, the lower the training loss, the better the model’s performance.

The purpose of training loss is to find weights and biases that have a low loss or to reduce them. There are many ways to achieve the desired training loss in a model. Some of these ways include:

  • Using transfer learning.
  • Deploying data augmentation.
  • Applying embeddings and checkpoints 
  • Allowing early stopping.
  • Embracing fast data pipelines.

What is validating loss in neural networks?

After training or splitting data, validating loss calculates the validation sets of data. The loss is based on training and validation to interpret and optimize a model. If training loss is good, your validation loss is generalized and should be significant to the result of your training loss. If your validation loss is lower compared to your training loss, it means your data training has been split wrongly.

Which loss function is best for classification?

For regression loss functions, the most common function is the Mean-Squared Error (MSE). This ubiquity is because the MSE measures errors in simple steps. It provides the results of the average of squared errors and bases their prediction on estimated and actual values.

For classification loss functions, however, the most common function is the Cross-Entropy Loss (CEL). This function owes its popularity to how it predicts output from a set of finite categorical values. It shows the divergence between two probability distributions and their relative entropy. 

How do you decide which loss function to use for Deep and Machine Learning? 

Most times, you don’t know which loss function to use for Machine Learning. This confusion is not because loss functions are complex; it is, however, because they are subjective and not general. If you’re faced with that sort of situation, here are things to consider:

  • Problem you’re solving: The problem you’re solving should inform the loss function to use for Machine Learning. It follows your prediction models or anything at all you’re trying to model.
  • Metric you’re using: Metrics should optimize loss functions. Not only that, they should complement as well. You can use cost functions to influence the right metrics into your algorithm.
  • Costs involved: The costs involved in building and shaping your model will inform your loss function. If the cost is higher compared to the effort and result, you should go for a more cost-effective loss function. Another cost function vs loss function scenario.


Loss functions in Machine Learning show the relationship between the estimated value or a model and its actual value. The relationship can either be measured using regression loss functions or classification loss functions. Regardless, the uses of loss functions are explicit in the prediction of models and understanding of their performance. 

Join the SDS Club to have access to hundreds of courses and be a part of a growing community of data scientists. 

Subscribe to our newsletter to get real time updates on Data Science industry trends and best practices. 

 Also, share this post with your friends on social media. Let the good go round!


A million students have already chosen SuperDataScience

It’s time for you to Join the Club!