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ENCAS: Evolutionary Neural Cascade Search across Supernetworks (Best Paper @ GECCO 2022)



ENCAS is a NAS algorithm for efficiently searching network architectures to be combined in a cascade. It utilizes multiple pretrained supernetworks that have different operations and search spaces. Our algorithm is multiobjective: in a single run, it finds many models with different trade-offs between accuracy and FLOPS.

This repo contains the code for our paper Evolutionary Neural Cascade Search across Supernetworks, which includes ENCAS, ENCAS-joint, and reproduction of Neural Architecture Transfer.


This is a subset of our results, see the paper for others.

Comparison with other NAS approaches

On CIFAR-10 and ImageNet ENCAS dominates previous approaches; on CIFAR-100 ENCAS is better than previous NAS approaches, on par with EfficientNet B0-B2, and worse than B3.

Applying ENCAS to timm models

ENCAS can be used to search for cascades of arbitrary models: we applied it to 518 models from timm (PyTorch image models, and achieved a dominating trade-off front.

Reproducing the results

General notes

Setting seed doesn't lead to complete reproducibility because to achieve it, PyTorch needs to be restricted to deterministic operations, which negatively affects speed. However, the results should be very close in terms of metrics (since for our paper we ran each experiment 10 times).

Since NAT spends roughly half of the time not using GPU, the code was written to allow 2 runs to use a single GPU (this is achieved by only working with GPU in subprocesses, which are killed once they are done, allowing the next subprocess to use the entire VRAM).

The data of all our experiments (including the supernetwork weights) is available here.


Clone the repo.

Set PYTHONPATH: export PYTHONPATH=PATH_TO_ENCAS, where PATH_TO_ENCAS is the path where you cloned ENCAS (e.g. "/export/scratch3/aleksand/encas").

Put the pretrained supernetworks into the 'data' folder (put the two OFA supernetworks into a subfolder "ofa", rename them to supernet_w1.0 and supernet_w1.2). Links:

Set "NAT_PATH" in to the full path to the directory where you cloned this repo.

To create ImageNet validation set, Download ImageNetV2 and combine the three datasets, removing duplicates. You should get 20,683 images.

To store labels of validation & test sets for the search, run python data_utils/

Clone the MO-GOMEA repo & follow the instructions there to compile it.

Conda environment

Create conda envronment from the data/env_encas.yml.

Then, run:

pip install git+
pip install git+

(these are my forks of those repos with a couple of minor bugs fixed)

Finally, activate the environment.

(Don't forget to check that your GPU can be used by Pytorch)

Reproducing Neural Architecture Transfer (NAT)

Configs: configs_nat/cifar[10|100]_reproducenat.yml

Change data (path to the dataset), path_logs (path to the logs folder), n_runs (how many runs/seeds).

Run python --config configs_nat/cifar10_reproducenat.yml

NAT with better hyperparameters (for ENCAS)

Configs: configs_nat/[cifar10|cifar100|imagenet]_r0_[alpha|attn|ofa10|ofa12|proxyless]_sep.yml

Change data (path to the dataset), path_logs (path to the logs folder), n_runs (how many runs/seeds).

Run python --config configs_nat/cifar10_r0_alpha_sep.yml for the dataset and the supernetwork of your choice.


Configs: configs_nat/cifar[10|100]_r0_[alphaofa|5nets].yml

Change data (path to the dataset), path_logs (path to the logs folder), n_runs (how many runs/seeds), gomea_exe (path to the MO-GOMEA executable you compiled).

Run python --config configs_nat/cifar10_r0_5nets.yml. The included configs are either for all 5 supernetworks or for AlphaNet+OFA-w1.2, but any combination of the supernetworks can be used.


Configs: configs_encas/[c10|c100|img]_5nets.yml

Make sure that all the relevant supernetworks have been trained with NAT (see above).

Run python encas/ --config configs_encas/c10_5nets.yml

There are additional configs for running baselines: "_greedy" for GreedyCascade (, "_random" for random search. Also, configs with "_ens" are for searching ensembles instead of cascades.


Configs: configs_encas/[c10|c100|img]_5nets_join.yml

Make sure that ENCAS-joint has finished (see above).

In after_search/ modify the parameters passed to the extract_store_eval and execute python after_search/

Run python encas/ --config configs_encas/c10_5nets_join.yml

ENCAS for timm models

Config: configs_encas/timm.yml

In after_search/ modify the path to ImageNet. Run python after_search/ to save the outputs of timm models on validation and test.

Run python encas/ --config configs_encas/timm.yml


The code to reproduce the figures in our paper is also published. Once you have run the experiments referenced in a figure, you can create the figure by uncommenting & running the relevant lines in plot_results/plot_results_[cifar10|cifar100|imagenet] (the figure numbers are mentioned in the code).


	author = {Chebykin, Alexander and Alderliesten, Tanja and Bosman, Peter A. N.},
	title = {Evolutionary Neural Cascade Search across Supernetworks},
	year = {2022},
	isbn = {9781450392372},
	publisher = {Association for Computing Machinery},
	address = {New York, NY, USA},
	url = {},
	doi = {10.1145/3512290.3528749},
	booktitle = {Proceedings of the Genetic and Evolutionary Computation Conference},
	pages = {1038–1047},
	numpages = {10},
	series = {GECCO '22}

Acknowledgments for code

We relied in large part on the code for NsgaNetV2 (, as well as on the parts of the NAT codebase privately provided to us by Zhichao Lu, for which we are very grateful.

The supernetworks' code is taken from the corresponding repos: OFA (, AlphaNet (, AttentiveNAS (