Dear Maintainer,

your package depends on libeigen3-dev. The upstream released a
new major version of this mathematical library, 5.0.0. Some
basic information about new features and changes in this version
can be found here:

https://libeigen.gitlab.io/releases/5.0/

This is a major version change and may require code changes in packages
depending on eigen3. The key breaking changes include:

  - Minimum required C++ standard is now C++14
  - Changes in the build system integration
  - Some API name changes

mrtrix3 FTBFS with libeigen3-dev 5.0.1. The full build log is available at:

https://debusine.debian.net/debian/developers-gladk-eigen3/artifact/3758084/

Here is the most probably relevant part of the failing build log:
    ===========================================

Checking for Eigen3 library:
ERROR: error compiling Eigen3 application!

    MRtrix3 was unable to compile a test program involving Eigen3.

  Set the EIGEN_CFLAGS environment variable to inform 'configure' of
  the flags it must provide to the compiler in order to compile
  programs that use Eigen3 functionality; this may include the path to
  the Eigen3 include files, as well as any required flags.
  For example:
    $ export EIGEN_CFLAGS="-isystem /usr/include/eigen3"
    $./configure
  (amend with the actual path to the Eigen3 include files on your system)

make[1]: *** [debian/rules:36: override_dh_auto_configure] Error 1
make[1]: Leaving directory '/build/reproducible-path/mrtrix3-3.0.8'
make: *** [debian/rules:33: binary-arch] Error 2
dpkg-buildpackage: error: debian/rules binary-arch subprocess failed with exit status 2

    ===========================================
libeigen3-dev_5.0.1-1 is available in experimental.

When this package version lands into unstable (probably at the beginning
of June 2026), this bug will be increased in severity to serious.

Thanks,

Anton

We believe that the bug you reported is fixed in the latest version of
mrtrix3, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1136250@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Andreas Tille <tille@debian.org> (supplier of updated mrtrix3 package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Thu, 11 Jun 2026 22:03:57 +0200
Source: mrtrix3
Architecture: source
Version: 3.0.8-2
Distribution: unstable
Urgency: medium
Maintainer: Debian Med Packaging Team <debian-med-packaging@lists.alioth.debian.org>
Changed-By: Andreas Tille <tille@debian.org>
Closes: 1136250
Changes:
 mrtrix3 (3.0.8-2) unstable; urgency=medium
 .
   * Team upload.
   * Use C++14 for Eigen3 detection test, required by Eigen >= 3.4 / 5.0
     Closes: #1136250
   * Standards-Version: 4.7.4 (routine-update)
   * Reflow Uploaders field (cme)
   * Remove Priority field (cme)
   * Drop 'Rules-Requires-Root: no' from d/control (routine-update)
   * Reformat the Last-Update date as ISO YYYY-MM-DD.
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