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https://github.com/lucfra/FAR-HO
Gradient based hyperparameter optimization & meta-learning package for TensorFlow
https://github.com/lucfra/FAR-HO
gradient-descent hyperparameter-optimization optimization tensorflow
Last synced: 3 months ago
JSON representation
Gradient based hyperparameter optimization & meta-learning package for TensorFlow
- Host: GitHub
- URL: https://github.com/lucfra/FAR-HO
- Owner: lucfra
- License: mit
- Created: 2017-12-04T21:42:43.000Z (almost 7 years ago)
- Default Branch: master
- Last Pushed: 2020-03-24T12:22:57.000Z (over 4 years ago)
- Last Synced: 2024-06-25T05:35:32.286Z (5 months ago)
- Topics: gradient-descent, hyperparameter-optimization, optimization, tensorflow
- Language: Jupyter Notebook
- Homepage:
- Size: 505 KB
- Stars: 187
- Watchers: 13
- Forks: 48
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
- awesome-deep-learning-tools - FAR-HO - learning package for TensorFlow (2.For Experiment / Hyperparameter Tuning)
README
# FAR-HO
Gradient-based hyperparameter optimization and meta-learning package based on [TensorFlow](https://www.tensorflow.org/)
This is the new package that implements the algorithms presented in the paper
[_Forward and Reverse Gradient-Based Hyperparameter Optimization_](http://proceedings.mlr.press/v70/franceschi17a). For the older package see [RFHO](https://github.com/lucfra/RFHO). FAR-HO [features simplified interfaces, additional
capabilities and a tighter integration with `tensorflow`](https://github.com/lucfra/FAR-HO#new-features-and-differences-from-rfho).
- Reverse hypergradient (`ReverseHG`), generalization of algorithms presented in Domke [2012] and MacLaurin et Al. [2015] (without reversable dynamics and "reversable dtype"); including the "truncated reverse version" `ReverseHG.truncated`, see [_Truncated Back-propagation for Bilevel Optimization_](https://arxiv.org/abs/1810.10667)
- Forward hypergradient (`ForwardHG`)
- Online versions of the two previous algorithms: Real-Time HO (RTHO) and Truncated-Reverse HO (TRHO)
- Implicit differentiation (`ImplicitHG`), which can be used to implement [HOAG algorithm](http://proceedings.mlr.press/v48/pedregosa16) [Pedregosa, 2016]
These algorithms algorithms compute, with different procedures, the (approximate) gradient
of an outer objective such as a validation error with respect
to the outer variables (e.g. hyperparameters).
We call the gradient of the outer objective _hypergradient_.
The "online" algorithms may perform several updates of the
outer variables before reaching the final iteration, and are in general are much faster then their "batch" version. This procedure is linked to warm restart for solving the inner optimizaiton problem, but the hypergradient is, in general, biased.
**IMPORTANT NOTE:** This is not a plug-and-play hyperparameter optimizaiton package, but rather a research package that collects some useful methods that aim at simplifying the creation of experiments in gradient-based hyperparameter optimizaiton and related areas. With respect to other HPO packages, here a more specific problem structure is required. Furthermore, depending on the specific problem, the performance may be somewhat sensiteve to algorithmic parameters. As an important example, the inner optimizaion dynamics *should not diverge* in order for the hypergradients to yield useful informations [ Troubleshooting section coming soon! ].
**NOTE II:** In Italian FARO means beacon or lighthouse (so... no "H", but the "H" in Italian is silent!) .
These algorithms are useful also in meta-learning where parameters of various _meta-learners_ effectively play the role
of outer variables, as explained here in the workshop paper
[_A Bridge Between Hyperparameter Optimization and Learning-to-learn_](https://arxiv.org/abs/1712.06283).
and [_Bilevel Programming for Hyperparameter Optimization and Meta-Learning_](http://proceedings.mlr.press/v80/franceschi18a/franceschi18a.pdf)
This package is also described in the workshop paper
[_ Far-HO: A Bilevel Programming Package for Hyperparameter Optimization and Meta-Learning_]( https://arxiv.org/abs/1806.04941)
presented at [AutoML 2018](https://sites.google.com/site/automl2018icml/) at ICML
## Installation & Dependencies
Clone the repository and run setup script.
```
git clone git clone https://github.com/lucfra/FAR-HO.git
cd FAR-HO
python setup.py install
```
Beside "usual" packages (`numpy`), FAR-HO is built upon `tensorflow`.
Some examples depend on the package [`experimet_manager`](https://github.com/lucfra/ExperimentManager)
while automatic dataset download (Omniglot) requires `datapackage`.
Please note that required packages will not be installed automatically.
## Overview
Aim of this package is to implement and develop gradient-based hyperparameter optimization (HO) techniques in
TensorFlow, thus making them readily applicable to deep learning systems.
This optimization techniques find also natural applications in the field of meta-learning and
learning-to-learn.
Feel free to issues comments, suggestions and feedbacks! You can email me at [email protected] .
#### Quick Start
- [Self contained example](https://github.com/lucfra/FAR-HO/blob/master/far_ho/examples/Example_weighted_error(and_lr_and_w0).ipynb) on MNIST with `ReverseHG` for the optimization of initial starting point (inital weights), weights of each example and learning rate.
- [IPython notebook](https://github.com/lucfra/FAR-HO/blob/master/far_ho/examples/autoMLDemos/Far-HO%20Demo%2C%20AutoML%202018%2C%20ICML%20workshop.ipynb)
that showcase the usage of `ReverseHG`, `ForwardHG` and online `ForwardHG` (RTHO algorithm) in simple settings
- _Coming soon_: What you can and cannot do with this package.
- [Hyper-representation](https://github.com/lucfra/FAR-HO/blob/master/far_ho/examples/hyper_representation.py) and related [notebook](https://github.com/lucfra/FAR-HO/blob/master/far_ho/examples/Hyper%20Representation_experiments.ipynb): an example in the context of learning-to-learn. In this case the hyperparameters are some of the weights of a convolutional neural network (plus the learning rate!).
The idea is to learn a cross-episode shared representation by explicitly minimizing the mean generalization error over meta-training tasks. See [A bridge between hyperparameter optimization and learning-to-Learn](https://arxiv.org/abs/1712.06283) presentied at [Workshop on meta-learning](http://metalearning.ml/). _Note_: for the moment, for running the code for this experiment you need to install the package https://github.com/lucfra/ExperimentManager for data management and statistics recording.
- See also [this experiments package](https://github.com/prolearner/hyper-representation) for code for reproducing few-shot experiments
presented in ICML 2018 paper.
#### Core Steps
- Create a model1 with TensorFlow
- Create the hyperparameters you wish to optimize2 with the function `get_hyperparameter` (which could be also variables of your model)
- Define an inner objective (e.g. a training error) and an outer objective (e.g. a validation error) as scalar `tensorflow.Tensor`
- Create an instance of `HyperOptimizer` after choosing an hyper-gradient computation algorithm among
`ForwardHG`, `ReverseHG` and `ImplicitHG` (see next section)
- Call the function `HyperOptimizer.minimize` specifying passing the outer and inner objectives,
as well as an optimizer for the outer problem (which can be any optimizer form `tensorflow`)
and an optimizer for the inner problem (which must be an optimizer contained in this package;
at the moment gradient descent, gradient descent with momentum and Adam algorithms are available,
but it should be quite straightforward to implement other optimizers, email me if you're interested!)
- Execute `HyperOptimizer.run(T, ...)` function inside a `tensorflow.Session`,
optimize inner variables (parameters) and perform a step of optimization of outer variables (hyperparameter).
Two scripts in the folder [autoMLDemos](https://github.com/lucfra/FAR-HO/tree/master/far_ho/examples/autoMLDemos)
showcase typical usage of this package
```python
import far_ho as far
import tensorflow as tf
model = create_model(...)
lambda1 = far.get_hyperparameter('lambda1', ...)
lambda1 = far.get_hyperparameter('lambda2', ...)
io, oo = create_objective(...)
inner_problem_optimizer = far.GradientDescentOptimizer(lr=far.get_hyperparameter('lr', 0.1))
outer_problem_optimizer = tf.train.AdamOptimizer()
farho = far.HyperOptimizer()
ho_step = farho.minimize(oo, outer_problem_optimizer,
io, inner_problem_optimizer)
T = 100
with tf.Session().as_default():
for _ in range(100):
ho_step(T)
```
____
1 This is gradient-based optimization and for the computation
of the hyper-gradients second order derivatives of the training error show up
(_even tough no Hessian matrix is explicitly computed at any time_);
therefore, all the ops used
in the model should have a second order derivative registered in `tensorflow`.
2 For the hyper-gradients to make sense, hyperparameters should be
real-valued. Moreover, while `ReverseHG` should handle generic r-rank tensor
hyperparameters, `ForwardHG`requires scalars hyperparameters. Use the keyword argument `scalar=True` in `get_hyperparameter` for obtaining a scalr splitting of a general tensor.
#### Which Algorithm Do I Choose?
Forward and Reverse-HG compute the same hypergradient, so
the choice is a matter of time versus memory!
The online versions of the algorithms can dramatically speed-up the optimization.
#### The Idea Behind: Hyperparameter Optimization
The objective is to minimize some validation function _E_ with respect to
a vector of hyperparameters _lambda_. The validation error depends on the model output and thus
on the model parameters _w_.
_w_ should be a minimizer of the training error and the hyperparameter optimization
problem can be naturally formulated as a __bilevel optimization__ problem.
Since these problems are rather hard to tackle, we
explicitly take into account the learning dynamics used to obtain the model
parameters (e.g. you can think about stochastic gradient descent with momentum),
and we formulate
HO as a __constrained optimization__ problem. See the [paper](http://proceedings.mlr.press/v70/franceschi17a) for details.
#### New features and differences from RFHO
- __Simplified interface__: optimize paramters and hyperparamters with "just" a call of `far.HyperOptimizer.minimize`, create variables designed as hyperparameters with `far.get_hyperparameter`, no more need to vectorize the model weights, `far.optimizers` only need to specify the update as a list of pairs (v, v_{k+1})
- __Additional capabilities__: set an initalizaiton dynamics and optimize the (dsitribution) of initial weights, allowed explicit dependence of the outer objective w.r.t. hyperparameters, support for multiple outer objectives and multiple inner problems (episode batching, average the sampling from distributions, ...)
- __Tighter integration__: collections for hyperparameters and hypergradients (use `far.GraphKeys`), use out-of-the-box models (no need to vectorize the model), use any TensorFlow optimizer for the outer objective (validation error)
- Lighter package: only code for implementing the algorithms and running the examples
- Forward hypergradient methods have been reimplemented with a [double reverse mode trick](https://j-towns.github.io/2017/06/12/A-new-trick.html), thanks to Jamie Townsend.
### Citing
If you use this package please cite
```latex
@InProceedings{franceschi2017forward,
title = {Forward and Reverse Gradient-Based Hyperparameter Optimization},
author = {Luca Franceschi and Michele Donini and Paolo Frasconi and Massimiliano Pontil},
booktitle = {Proceedings of the 34th International Conference on Machine Learning},
pages = {1165--1173},
year = {2017},
volume = {70},
series = {Proceedings of Machine Learning Research},
publisher = {PMLR},
pdf = {http://proceedings.mlr.press/v70/franceschi17a/franceschi17a.pdf},
}
```
##### Works on meta-learning
```latex
@InProceedings{franceschi2018bilevel,
title = {Bilevel Programming for Hyperparameter Optimization and Meta-learning},
author = {Luca Franceschi and Paolo Frasconi and Saverio Salzo and Riccardo Grazzi and Massimiliano Pontil},
booktitle = {Proceedings of the 35th International Conference on Machine Learning (ICML 2018},
year = {2018},
series = {Proceedings of Machine Learning Research},
publisher = {PMLR},
pdf = {http://proceedings.mlr.press/v80/franceschi18a/franceschi18a.pdf},
}
```
```latex
@article{franceschi2017bridge,
title={A Bridge Between Hyperparameter Optimization and Larning-to-learn},
author={Franceschi, Luca and Frasconi, Paolo and Donini, Michele and Pontil, Massimiliano},
journal={arXiv preprint arXiv:1712.06283},
year={2017}
}
```
This package has been used for the project [LDS-GNN](https://github.com/lucfra/LDS-GNN): the code for the ICML 2019 paper ["Learning Discrete Structures for Graph Neural Networks"](https://arxiv.org/abs/1903.11960).