Since binaries are sometimes not compatible across different versions of macOS and due to increasing security measures of Apple, some extra work might be required to get MTEX running on macOS.

library load disallowed by system policy

If you experience the following error message

Invalid MEX-file 'some path to
mtex/mtex-5.3/extern/nfft/nfsoftmex.mexmaci64': dlopen(some path to
mtex//mtex-5.3/extern/nfft/nfsoftmex.mexmaci64, 6): no suitable image
found.  Did find:
some path to mtex/mtex-5.3/extern/nfft/nfsoftmex.mexmaci64: code
signature in (some path to
mtex/mtex-5.3/extern/nfft/nfsoftmex.mexmaci64) not valid for use in
process using Library Validation: library load disallowed by system policy

you can either download MTEX with a command line tool such as curl or wget

curl -LJO --output mtex.zip https://github.com/mtex-toolbox/mtex/releases/download/mtex-5.3/mtex-5.3.zip

or, if you have downloaded MTEX with a browser, type in Matlab

!sudo xattr -r -d com.apple.quarantine /path/to/mtexfolder

Unable to compile mex files during startup_mtex

If you (still) get the following error, you will need to recompile the mex files on your own. MTEX tries to perform the compilation automatically. However, in some case you might experience error messages like

Error: unable to compile mex files during startup_mtex e.g.:

Checking mex files failed!
 > Trying now to recompile mex files.
 > In mex_install (line 15)
   In check_installation>check_mex (line 69)
   In check_installation (line 33)
   In startup_mtex (line 66)
   In startup (line 7)
... compiling S1Grid_find.c
Building with 'Xcode with Clang'.
Compiling some path to mtex/mtex-5.3/mex/S1Grid_find.c failed!

or

 >   MTEX: Couldn't get the mex files working!
 >   The original error message was:
 >   Invalid MEX-file
 > 'some path to mtex/mtex-5.3/mex/SO3Grid_dist_region.mexmaci64':
 > dlopen(some path to mtex/mtex-5.3/mex/SO3Grid_dist_region.mexmaci64,
 > 6): Library not loaded: @loader_path/libmex.dylib
 >   Referenced from:
 > some path to mtex/mtex-5.3/mex/SO3Grid_dist_region.mexmaci64
 >   Reason: image not found
 >   Contact author for help!
  1. Make sure that after upgrading your system, to also upgrade xcode (via appstore) and install the command line tools and accept the licence by
    sudo xcodebuild -license accept
    xcode-select --install
    
  2. You might need to modify the compiler options used by Matlab. The configuration file can be found by the command
    m  = mex.getCompilerConfigurations
    m.MexOpt
    ans =
       /Users/rk/Library/Application/MathWorks/MATLAB/R2019b/mex_C_maci64.xml
    

    The exact file name depends on the compiler installed on your system, e.g. /Applications/MATLAB_R2019a.app/bin/maci64/mexopts/clang_maci64.xml. Within the configuration file change the lines

   <SDKVER>
      <cmdReturns name="xcrun -sdk macosx --show-sdk-version"/>
   </SDKVER>

to

   <SDKVER>
      <cmdReturns name="xcrun -sdk macosx --show-sdk-version  | cut -c1-5"/>
   </SDKVER>

and do from within Matlab

mex -setup C

Now startup_mtex.m will hopefully run without any trouble.

Compiling the nfft

1. Install gcc with openmp and libtools

Using homebrew is probably the easiest

brew install gcc libtool

2. Get nfft source from github

git clone https://github.com/NFFT/nfft/tree/develop
./bootstrap.sh

3. Set the compilation parameters

The path to gcc and matlab depends on your system and should be set accordingly

CC=/usr/local/Cellar/gcc/8.2.0/bin/gcc-8
LDFLAGS=-Wl,-L/usr/local/Cellar/gcc/8.2.0/lib/gcc/8
./configure --with-matlab=/Applications/MATLAB_R2018b.app --enable-nfsoft\
  --enable-nfsft --enable-openmp --enable-portable-binary\
  --with-apple-gcc-arch=x86_64 -

or if for some reason you can not use openMP

CC=/usr/local/Cellar/gcc/8.2.0/bin/gcc-8
LDFLAGS=-Wl,-L/usr/local/Cellar/gcc/8.2.0/lib/gcc/8
./configure --with-matlab=/Applications/MATLAB_R2018b.app --enable-nfsoft\
  --enable-nfsft --enable-portable-binary --with-apple-gcc-arch=x86_64

4. Compile the nfft

make

The easists way is to make out of the following lines an executable shell script. Please do not forget to include the definitions of gcc and Matlab pathes from above

#!/bin/bash
CC=/usr/local/Cellar/gcc/8.2.0/bin/gcc-8
MATLABDIR=/Applications/MATLAB_R2018b.app

for LIB in nfft nfsft nfsoft nnfft fastsum nfct nfst do
  cd matlab/"$LIB"
  "$CC" -o .libs/lib"$LIB".mexmaci64 -bundle .libs/lib"$LIB"_la-"$LIB"mex.o \
    -Wl,-force_load,../../.libs/libnfft3_matlab.a \
    -Wl,-force_load,../../matlab/.libs/libmatlab.a \
    -L"$MATLABDIR"/bin/maci64 -lm -lmwfftw3 -lmx -lmex \
    -lmat -fopenmp -O3 -malign-double -march=core2 \
    -arch x86_64 -fopenmp -static-libgcc
  cp .libs/lib"$LIB".mexmaci64 "$LIB"mex.mexmaci64
  cd ../..
done

the vesion without openMP

#!/bin/bash
CC=/usr/local/Cellar/gcc/8.2.0/bin/gcc-8
MATLABDIR=/Applications/MATLAB_R2018b.app

for LIB in nfft nfsft nfsoft nnfft fastsum nfct nfst do
  cd matlab/"$LIB"
  "$CC" -o .libs/lib"$LIB".mexmaci64 -bundle .libs/lib"$LIB"_la-"$LIB"mex.o \
    -Wl,-force_load,../../.libs/libnfft3_matlab.a \
    -Wl,-force_load,../../matlab/.libs/libmatlab.a \
    -L"$MATLABDIR"/bin/maci64 -lm -lmwfftw3 -lmx -lmex \
    -lmat -O3 -malign-double -march=core2 \
    -arch x86_64 -static-libgcc
  cp .libs/lib"$LIB".mexmaci64 "$LIB"mex.mexmaci64
  cd ../..
done

6. Copy the generated mex-files into the MTEX installation

make install

for mtex, copy the two files

matlab/nfsft/.libs/libnfsft.mexmaci64
matlab/nfsoft/.libs/libnfsoft.mexmaci64

into your mtex installation into

mtex/extern/nfft_openMP/

or

mtex/extern/nfft/