# AI News, Hyperopt tutorial for Optimizing Neural Networks’ Hyperparameters

- On Wednesday, August 1, 2018
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## Hyperopt tutorial for Optimizing Neural Networks’ Hyperparameters

It is hence a good method for meta-optimizing a neural network which is itself an optimisation problem: tuning a neural network uses gradient descent methods, and tuning the hyperparameters needs to be done differently since gradient descent can’t apply.

Therefore, Hyperopt can be useful not only for tuning hyperparameters such as the learning rate, but also to tune more fancy parameters in a flexible way, such as changing the number of layers of certain types, or the number of neurons in a layer, or even the type of layer to use at a certain place in the network given an array of choices, each with nested tunable hyperparameters.

parameter is defined with a certain uniformrange or else a probability distribution, such as: There is also a few quantized versions of those functions, which rounds the generated values at each step of “q”: It is also possible to use a “choice” which can lead to hyperparameter nesting: Visualisations of the parameters for probability distributions can be found below.

That’s because we want to observe changes in the learning rate according to changing it with multiplications rather than additions, e.g.: when adjusting the learning rate, we’ll want to try to divide it or multiply it by 2 rather than adding and substracting a finite value.

In [6]: Here are the space and results of the 3 first trials (out of a total of 1000): What interests us most is the ‘result’ key of each trial(here, we show 7): Note that the optimization could be parallelized by using MongoDB and storing the trials’ state here.

- On Wednesday, August 1, 2018
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## Automated Machine Learning Hyperparameter Tuning in Python

Now, let’s define the entire domain: Here we use a number of different domain distribution types: (There are other distributions as well listed in the documentation.) There is one important point to notice when we define the boosting type: Here we are using a conditional domain which means the value of one hyperparameter depends on the value of another.

During optimization, the TPE algorithm constructs the probability model from the past results and decides the next set of hyperparameters to evaluate in the objective function by maximizing the expected improvement.

However, if we want to find out what is going on behind the scenes, we can use a Trials object which will store basic training information and also the dictionary returned from the objective function (which includes the loss andparams ).

Before training we open a new csv file and write the headers: and then within the objective function we can add lines to write to the csv on every iteration (the complete objective function is in the notebook): Writing to a csv means we can check the progress by opening the file while training (although not in Excel because this will cause an error in Python.

Once we have the four parts in place, optimization is run with fmin : Each iteration, the algorithm chooses new hyperparameter values from the surrogate function which is constructed based on the previous results and evaluates these values in the objective function.

The best object that is returned from fmin contains the hyperparameters that yielded the lowest loss on the objective function: Once we have these hyperparameters, we can use them to train a model on the full training data and then evaluate on the testing data (remember we can only use the test set once, when we evaluate the final model).

If the algorithm finds a local minimum of the objective function, it might concentrate on hyperparameter values around the local minimum rather than trying different values located far away in the domain space.

- On Wednesday, August 1, 2018
- By Read More

## Hyperopt tutorial for Optimizing Neural Networks’ Hyperparameters

It is hence a good method for meta-optimizing a neural network which is itself an optimisation problem: tuning a neural network uses gradient descent methods, and tuning the hyperparameters needs to be done differently since gradient descent can’t apply.

Therefore, Hyperopt can be useful not only for tuning hyperparameters such as the learning rate, but also to tune more fancy parameters in a flexible way, such as changing the number of layers of certain types, or the number of neurons in a layer, or even the type of layer to use at a certain place in the network given an array of choices, each with nested tunable hyperparameters.

parameter is defined with a certain uniformrange or else a probability distribution, such as: There is also a few quantized versions of those functions, which rounds the generated values at each step of “q”: It is also possible to use a “choice” which can lead to hyperparameter nesting: Visualisations of the parameters for probability distributions can be found below.

That’s because we want to observe changes in the learning rate according to changing it with multiplications rather than additions, e.g.: when adjusting the learning rate, we’ll want to try to divide it or multiply it by 2 rather than adding and substracting a finite value.

In [6]: Here are the space and results of the 3 first trials (out of a total of 1000): What interests us most is the ‘result’ key of each trial(here, we show 7): Note that the optimization could be parallelized by using MongoDB and storing the trials’ state here.

- On Wednesday, August 1, 2018
- By Read More

## Tuning Hyperparameters (part II): Random Search on Spark

In this part II of this series, I am continuing my take on hyperparameters optimisations strategies, this time I want to have a closer look at Random Search from the point of view of Spark.

No matter how well you designed your algorithms, how beautiful the mathematics may be, if the client requires a relative short training time on a huge volume of data, you better find a way to deliver!

Spark is a popular open-source framework for distributed computing on a cluster offering a wide library for manipulating Databases, streaming, distributed graph processing and most importantly for this discussion Machine Learning, i.e.

From a practical Machine Learning’s perspective, MMLSpark most notable feature is the access to the extreme gradient boosting library Lighgbm, which is the go-to quick-win approach to most Data Science Proof of Concepts.

Breeze is a popular scala library for numerical processing with a great variety of distributions within breeze.stats.distributions. For example, in the case a logistic regression we might want to define the following sampling space, On one hand, we wish to sample from a distribution, on the other in the case of a set of categorical choice, we should be able to set an Array of choice.

- On Monday, September 23, 2019

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