diff --git a/.travis.yml b/.travis.yml
index 947353ab..a81c0fbb 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,6 +15,7 @@ rvm:
   - 2.1.8
   - 2.2.4
   - 2.3.0
+  - 2.4.2
   - ruby-head
   # The latest stable and head versions built by clang
   - 2.3.0-clang
diff --git a/History.txt b/History.txt
index f6462d19..fe50df54 100644
--- a/History.txt
+++ b/History.txt
@@ -888,3 +888,22 @@
   * Fixed gem installation problem caused by mkmf
     abstraction (by @mrkn)
 
+=== 0.2.4 / 2017-12-14
+
+* No major enhancements.
+
+* 2 minor enhancements:
+
+  * Eliminated code reuse in math.rb between JRuby and MRI
+    versions of library (by @prasunanand)
+
+  * Slightly simplified #positive_definite? (by
+    @prasunanand)
+
+* 2 bug fixes:
+
+  * Fixed compilation problem on Mac OS X High Sierra (by
+    @mohawkjohn)
+
+  * Fixed failing #block_diagonal spec (due to missing
+    Array#sum) (by @mohawkjohn)
diff --git a/Manifest.txt b/Manifest.txt
index c173c684..ed443c2c 100644
--- a/Manifest.txt
+++ b/Manifest.txt
@@ -13,6 +13,16 @@ travis.sh
 .travis.yml
 lib/nmatrix.rb
 lib/nmatrix/atlas.rb
+lib/nmatrix/blas.rb
+lib/nmatrix/enumerate.rb
+lib/nmatrix/homogeneous.rb
+lib/nmatrix/math.rb
+lib/nmatrix/mkmf.rb
+lib/nmatrix/monkeys.rb
+lib/nmatrix/nmatrix.rb
+lib/nmatrix/shortcuts.rb
+lib/nmatrix/version.rb
+lib/nmatrix/yale_functions.rb
 lib/nmatrix/fftw.rb
 lib/nmatrix/lapack_core.rb
 lib/nmatrix/lapack_ext_common.rb
@@ -25,17 +35,14 @@ lib/nmatrix/io/mat_reader.rb
 lib/nmatrix/io/point_cloud.rb
 lib/nmatrix/io/fortran_format.rb
 lib/nmatrix/io/harwell_boeing.rb
-lib/nmatrix/blas.rb
-lib/nmatrix/enumerate.rb
-lib/nmatrix/homogeneous.rb
-lib/nmatrix/math.rb
-lib/nmatrix/mkmf.rb
-lib/nmatrix/monkeys.rb
-lib/nmatrix/nmatrix.rb
-lib/nmatrix/rspec.rb
-lib/nmatrix/shortcuts.rb
-lib/nmatrix/version.rb
-lib/nmatrix/yale_functions.rb
+lib/nmatrix/cruby/math.rb
+lib/nmatrix/jruby/decomposition.rb
+lib/nmatrix/jruby/enumerable.rb
+lib/nmatrix/jruby/error.rb
+lib/nmatrix/jruby/math.rb
+lib/nmatrix/jruby/nmatrix_java.rb
+lib/nmatrix/jruby/operators.rb
+lib/nmatrix/jruby/slice.rb
 ext/nmatrix/math/cblas_enums.h
 ext/nmatrix/math/cblas_templates_core.h
 ext/nmatrix/math/util.h
@@ -49,6 +56,14 @@ ext/nmatrix_atlas/math_atlas/gesdd.h
 ext/nmatrix_atlas/math_atlas/gesvd.h
 ext/nmatrix_atlas/math_atlas/inc.h
 ext/nmatrix_atlas/nmatrix_atlas.cpp
+ext/nmatrix_java/nmatrix/data/Complex.java
+ext/nmatrix_java/nmatrix/math/MathHelper.java
+ext/nmatrix_java/nmatrix/storage/dense/ArrayComparator.java
+ext/nmatrix_java/nmatrix/util/ArrayGenerator.java
+ext/nmatrix_java/nmatrix/util/MatrixGenerator.java
+ext/nmatrix_java/nmatrix/util/WrapperType.java
+ext/nmatrix_java/test/AssertTests.java
+ext/nmatrix_java/test/TestRunner.java
 ext/nmatrix_lapacke/extconf.rb
 ext/nmatrix_lapacke/lapacke.cpp
 ext/nmatrix_lapacke/lapacke/include/lapacke.h
diff --git a/Rakefile b/Rakefile
index d6a7152f..b7e36b7b 100644
--- a/Rakefile
+++ b/Rakefile
@@ -240,7 +240,7 @@ task :check_manifest do |task|
   manifest_files  = File.read("Manifest.txt").split
 
   git_files       = `git ls-files |grep -v 'spec/'`.split
-  ignore_files    = %w{.gitignore .rspec ext/nmatrix/binary_format.txt ext/nmatrix/ttable_helper.rb scripts/mac-brew-gcc.sh}
+  ignore_files    = %w{.gitignore .rspec ext/nmatrix/binary_format.txt scripts/ttable_helper.rb}
 
   possible_files  = git_files - ignore_files
 
diff --git a/ext/nmatrix_java/README.md b/ext/nmatrix_java/README.md
deleted file mode 100644
index e69de29b..00000000
diff --git a/ext/nmatrix_java/Rakefile b/ext/nmatrix_java/Rakefile
deleted file mode 100644
index 749578eb..00000000
--- a/ext/nmatrix_java/Rakefile
+++ /dev/null
@@ -1,68 +0,0 @@
-PROJECT_DIR = File.expand_path(".",Dir.pwd)
-# puts PROJECT_DIR
-
-BUILD_DIR = "build"
-CLASSES_DIR = "../build/classes"
-TEST_CLASSES_DIR = "build/testClasses"
-
-VENDOR_DIR = "#{PROJECT_DIR}/vendor"
-TARGET_DIR = "#{PROJECT_DIR}/target"
-# puts VENDOR_DIR
-
-jars = Dir["#{VENDOR_DIR}/*.jar"]
-# puts jars
-
-unless RUBY_PLATFORM == 'java'
-  abort 'Please run with JRuby'
-end
-
-#-----------------------------------------------------------------------------------------
-
-desc 'Compile java classes'
-task :javac do
-
-  Dir.chdir("nmatrix")
-  classes    = Dir['**/*.java']
-  sh "javac -classpath #{jars.join(':')} -d #{CLASSES_DIR} #{classes.join(' ')}"
-  # sh "javac -d #{CLASSES_DIR} #{classes.join(' ')}"
-
-end
-
-#-----------------------------------------------------------------------------------------
-desc 'Make jar file'
-task :jar do
-
-  Dir.chdir("build/classes")
-  classes = Dir['**/*.class']
-  # p classes
-  sh "jar -cf #{TARGET_DIR}/nmatrix.jar #{classes.join(' ')}"
-
-end
-
-#-----------------------------------------------------------------------------------------
-
-
-desc 'Compile test classes'
-task :compileTest do
-
-  classes    = Dir['**/*.java']
-  sh "javac -classpath #{jars.join(':')} -d #{TEST_CLASSES_DIR} #{classes.join(' ')}"
-  # sh "javac -d #{CLASSES_DIR} #{classes.join(' ')}"
-
-end
-
-#-----------------------------------------------------------------------------------------
-
-desc 'Run junit tests'
-task :test do
-
-  Dir.chdir("build/classes")
-  classes = Dir['**/*.class']
-  # p classes
-  sh "javac -classpath #{TARGET_DIR}/nmatrix.jar -d #{classes.join(' ')}"
-
-end
-
-#-----------------------------------------------------------------------------------------
-
-task :default => :javac
diff --git a/ext/nmatrix_java/nmatrix/data/Complex.java b/ext/nmatrix_java/nmatrix/data/Complex.java
deleted file mode 100644
index e69de29b..00000000
diff --git a/lib/nmatrix/mkmf.rb b/lib/nmatrix/mkmf.rb
index 2e2d0cd4..8c5d0526 100644
--- a/lib/nmatrix/mkmf.rb
+++ b/lib/nmatrix/mkmf.rb
@@ -91,8 +91,10 @@ def gplusplus_version
 $CXXFLAGS += " -O3 -std=#{$CXX_STANDARD} " #-fmax-errors=10 -save-temps
 #$CXXFLAGS += " -static -O0 -g -std=#{$CXX_STANDARD} "
 
-CONFIG['warnflags'].gsub!('-Wshorten-64-to-32', '') # doesn't work except in Mac-patched gcc (4.2)
-CONFIG['warnflags'].gsub!('-Wdeclaration-after-statement', '')
-CONFIG['warnflags'].gsub!('-Wimplicit-function-declaration', '')
-
+if CONFIG.has_key?('warnflags')
+  CONFIG['warnflags'].gsub!('-Wshorten-64-to-32', '') # doesn't work except in Mac-patched gcc (4.2)
+  CONFIG['warnflags'].gsub!('-Wdeclaration-after-statement', '')
+  CONFIG['warnflags'].gsub!('-Wimplicit-function-declaration', '')
+end
+  
 have_func("rb_array_const_ptr", "ruby.h")
diff --git a/lib/nmatrix/shortcuts.rb b/lib/nmatrix/shortcuts.rb
index 4400dcaa..07ff50fd 100644
--- a/lib/nmatrix/shortcuts.rb
+++ b/lib/nmatrix/shortcuts.rb
@@ -494,11 +494,11 @@ def block_diagonal(*params)
         block_sizes << b.shape[0]
       end
 
-      block_diag_mat = NMatrix.zeros(block_sizes.sum, options)
+      block_diag_mat = NMatrix.zeros(block_sizes.inject(0,:+), options)
       (0...params.length).each do |n|
         # First determine the size and position of the n'th block in the block-diagonal matrix
         block_size = block_sizes[n]
-        block_pos = block_sizes[0...n].sum
+        block_pos = block_sizes[0...n].inject(0,:+)
         # populate the n'th block in the block-diagonal matrix
         (0...block_size).each do |i|
           (0...block_size).each do |j|
diff --git a/nmatrix.gemspec b/nmatrix.gemspec
index e22f35dc..19ac5ad6 100644
--- a/nmatrix.gemspec
+++ b/nmatrix.gemspec
@@ -24,9 +24,9 @@ Gem::Specification.new do |gem|
 ***********************************************************
 Welcome to SciRuby: Tools for Scientific Computing in Ruby!
 
-NMatrix requires a C compiler, and has been tested only
-with GCC 4.6+. We are happy to accept contributions
-which improve the portability of this project.
+NMatrix requires a C/C++ compiler. Clang and GCC are 
+recommended. JRuby support is experimental, and requires
+Java.
 
 If you are upgrading from NMatrix 0.1.0 and rely on
 ATLAS features, please check the README.
diff --git a/scripts/mac-brew-gcc.sh b/scripts/mac-brew-gcc.sh
deleted file mode 100755
index 68888c9d..00000000
--- a/scripts/mac-brew-gcc.sh
+++ /dev/null
@@ -1,50 +0,0 @@
-#!/bin/bash
-
-# Script will not work for GCC 4.8 or 4.9. For those, please see
-# mac-mavericks-brew-gcc.sh
-
-VERSION="4.7.2" # Script should also work with GCC 4.7.1.
-PREFIX="/usr/gcc-${VERSION}"
-LANGUAGES="c,c++,fortran"
-MAKE="make -j 4"
-
-brew-path() { brew info $1 | head -n3 | tail -n1 | cut -d' ' -f1; }
-
-# Prerequisites
-
-brew install gmp mpfr libmpc
-
-# Next, download & install the latest GCC:
-
-mkdir -p $PREFIX
-mkdir temp-gcc
-cd temp-gcc
-wget ftp://ftp.gnu.org/gnu/gcc/gcc-$VERSION/gcc-$VERSION.tar.gz
-tar xfz gcc-$VERSION.tar.gz
-rm gcc-$VERSION.tar.gz
-cd gcc-$VERSION
-
-mkdir build
-cd build
-
-# Older versions of brew need brew-path instead of brew --prefix.
-../configure \
-     --prefix=$PREFIX \
-     --with-gmp=$(brew --prefix gmp) \
-     --with-mpfr=$(brew --prefix mpfr) \
-     --with-mpc=$(brew --prefix libmpc) \
-     --program-suffix=-$VERSION \
-     --enable-languages=$LANGUAGES \
-     --with-system-zlib \
-     --enable-stage1-checking \
-     --enable-plugin \
-     --enable-lto \
-     --disable-multilib
-
-$MAKE bootstrap
-
-make install
-
-# Uncomment for cleanup …
-# cd ../../..
-# rm -r temp-gcc
diff --git a/scripts/mac-mavericks-brew-gcc.sh b/scripts/mac-mavericks-brew-gcc.sh
deleted file mode 100644
index 867d050a..00000000
--- a/scripts/mac-mavericks-brew-gcc.sh
+++ /dev/null
@@ -1,22 +0,0 @@
-#!/bin/bash
-
-brew-path() { brew info $1 | head -n3 | tail -n1 | cut -d' ' -f1; }
-
-# Try using the following for GCC 4.9:
-#
-#   brew install gmp4 mpfr2 libmpc08 isl011 cloog018
-#
-#
-
-brew install gcc49 --enable-fortran
-# Source for this is: http://stackoverflow.com/questions/19535422/os-x-10-9-gcc-links-to-clang
-
-
-# You may wish to re-install your Ruby if you're using rbenv. To do
-# so, make sure you've installed openssl, readline, and libyaml.
-#
-# The commands for this are:
-#
-#    CC=gcc-4.8 RUBY_CONFIGURE_OPTS="--with-openssl-dir=`brew --prefix openssl` --with-readline-dir=`brew --prefix readline` --with-gcc=gcc-4.8 --enable-shared" rbenv install --keep 2.0.0-p247
-#
-#
\ No newline at end of file
diff --git a/ext/nmatrix/ttable_helper.rb b/scripts/ttable_helper.rb
similarity index 100%
rename from ext/nmatrix/ttable_helper.rb
rename to scripts/ttable_helper.rb