package owl-zoo

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OCaml Scientific and Engineering Computing - Zoo


Dune Dependency






Owl's Zoo System

The Zoo System is Owl's customised toplevel. It is used for scripting numerical applications and sharing small code snippets via gist among users. The Zoo system introduces a zoo directive into toplevel, the referred gist id will be automatically downloaded and imported as a module in the script. The nested zoo reference is also supported.

Published: 06 Dec 2019


Owl - OCaml Scientific and Engineering Computing

Owl is a dedicated system for scientific and engineering computing in the functional programming language OCaml.

This software is currently maintained by Komposio, a Helsinki-based software consulting company.

Visit the project website at

Optional features

You can enable optional features by setting the following variables to 1 before compilation:

  • OWL_ENABLE_EXPMODE=1: turn on experiment features like -flto

  • OWL_ENABLE_DEVMODE=1: turn on all the warnings in development

  • OWL_ENABLE_OPENMP=1: turn on OpenMP support in core module and the automatic parameter tuning (AEOS)

  • OWL_CFLAGS allows to change the default flags passed to the C targets, it defaults to

    OWL_CFLAGS="-g -O3 -Ofast -march=native -mfpmath=sse -funroll-loops -ffast-math -DSFMT_MEXP=19937 -msse2 -fno-strict-aliasing -Wno-tautological-constant-out-of-range-compare"`
  • OWL_AEOS_CFLAGS allows to change the default flags passed to the C targets when compiling AEOS. It defaults to

    OWL_AEOS_CFLAGS="-g -O3 -Ofast -march=native -funroll-loops -ffast-math -DSFMT_MEXP=19937 -fno-strict-aliasing"
  • OWL_DISABLE_LAPACKE_LINKING_FLAG=1 disables the -llapacke flag in the linking options. This is useful when you have lapacke installed on non-standard localtion.

If you are not using opam, you should run make clean before recompiling the library after having changed any of those environment variables.

For examples of use of this feature, you can refer to the Docker.ubuntu and Docker.ubuntu.arm docker files, or to the snippet in (which also shows how to use it within esy).


A common source of frustration when installing owl is the possible appearence of linking errors (see for example This usually happens when installing owl on ubuntu (where it depends on how openblas is complied and packaged), but could happen in other distributions (see for example The only way we could solve those issues is to recompile openblas and install it manually. You can see how we do it by looking at the Docker files in the repository:

Dependencies (4)

  1. owl = version
  2. ocaml-compiler-libs
  3. dune >= "1.7.0"
  4. ocaml >= "4.06.0" & < "4.14.0"

Dev Dependencies


Used by (1)

  1. owl-top < "0.9.0"




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