* installing *source* package ‘fCWTr’ ...
** package ‘fCWTr’ successfully unpacked and MD5 sums checked
** using staged installation
checking for gcc... clang -arch x86_64
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether the compiler supports GNU C... yes
checking whether clang -arch x86_64 accepts -g... yes
checking for clang -arch x86_64 option to enable C11 features... none needed
checking how to run the C preprocessor... clang -arch x86_64 -E
checking for brew... no
checking whether the compiler supports GNU C++... yes
checking whether clang++ -arch x86_64 -std=gnu++17 accepts -g... yes
checking for clang++ -arch x86_64 -std=gnu++17 option to enable C++11 features... none needed
checking for stdio.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for strings.h... yes
checking for sys/stat.h... yes
checking for sys/types.h... yes
checking for unistd.h... yes
checking for fftw3.h... yes
checking for library containing fftwf_free... no
configure: error: The fftw3 library is required.
ERROR: configuration failed for package ‘fCWTr’
* removing ‘/Volumes/Builds/packages/big-sur-x86_64/results/4.3/fCWTr.Rcheck/fCWTr’