# ERROR: error compiling Eigen3 application! for MAC **URL:** \ **Category:** Uncategorized\ **Created:** [March 1, 2021, 1:00pm UTC](https://community.mrtrix.org/t/error-error-compiling-eigen3-application-for-mac/4608 "2021-03-01T13:00:19Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![jdtournier](https://community.mrtrix.org/user_avatar/community.mrtrix.org/jdtournier/32/2594_2.png) [@jdtournier](https://community.mrtrix.org/u/jdtournier)\ **Post date:** [March 1, 2021, 5:06pm UTC](https://community.mrtrix.org/t/error-error-compiling-eigen3-application-for-mac/4608/2 "2021-03-01T17:06:46Z")
First point to note is that you’re using a [separate project, independent of MRtrix3](https://community.mrtrix.org/t/error-from-dwi2response/2818/5), which we don’t provide support for. We would generally suggest you install an official release of MRtrix3 before investigating. Nonetheless, I think in your case the issue is likely to be simply that the dash you used in the `EIGEN_CFLAGS="–isystem ..."` variable is a long em-dash, rather than the regular hyphen “`-`” (there are [many dashes in Unicode](https://www.compart.com/en/unicode/category/Pd), but only the ASCII hyphen / minus sign would be recognised as such). I suspect you may have copy/pasted that bit from a Word document or similar, which often decides to ‘upgrade’ hyphen to long dashes. – see e.g. [this post for details](https://community.mrtrix.org/t/trouble-with-mrmath/4158/2). To fix this, simply pull up that command again, and edit it to replace the dash with a minus sign that you’ve typed in from the keyboard. Hopefully that’ll be all that’s required here… --- _[View the full topic](https://community.mrtrix.org/t/error-error-compiling-eigen3-application-for-mac/4608)._