find_exec_file Function

function find_exec_file(filename) result(returned)
! look for file. If not found look for file.la. If not found, repeat using directories in MATRIX_PATH=DIR1:DIR2:DIR3...
character(len=*),intent(in)  :: filename
character(len=:),allocatable :: returned
   if(exists(filename))then
      returned=filename
   elseif(exists(trim(filename)//'.la'))then
      returned=filename//'.la'
   else
      returned=lookfor(filename,'LALA_PATH')
      if(returned.eq.'')then
         returned=lookfor(filename//'.la','LALA_PATH')
      endif
      if(returned.eq.'')returned=filename
   endif
end function find_exec_file