```cmake

if (DOWNLOAD_EXTERNALS)

  # Configure boost
  # ---------------
  # Note: a script is used to checkout a quasi minimal version
  set(DOWNLOAD_DIR ${EXTERNALS_DIR}/boost)

  ExternalProject_Add(boost
    DOWNLOAD_COMMAND svn co --depth files http://svn.boost.org/svn/boost/tags/release/Boost_1_50_0/boost
    DOWNLOAD_DIR ${DOWNLOAD_DIR}
    TMP_DIR ${DOWNLOAD_DIR}/tmp
    STAMP_DIR ${DOWNLOAD_DIR}/stamp
    UPDATE_COMMAND svn update
      ${DOWNLOAD_DIR}/boost/config
      ${DOWNLOAD_DIR}/boost/detail
      ${DOWNLOAD_DIR}/boost/exception
      ${DOWNLOAD_DIR}/boost/smart_ptr
      ${DOWNLOAD_DIR}/boost/algorithm
      ${DOWNLOAD_DIR}/boost/iterator
      ${DOWNLOAD_DIR}/boost/mpl
      ${DOWNLOAD_DIR}/boost/range
      ${DOWNLOAD_DIR}/boost/type_traits
      ${DOWNLOAD_DIR}/boost/preprocessor
      ${DOWNLOAD_DIR}/boost/utility
      ${DOWNLOAD_DIR}/boost/concept
      ${DOWNLOAD_DIR}/boost/function
      ${DOWNLOAD_DIR}/boost/bind
      ${DOWNLOAD_DIR}
    CONFIGURE_COMMAND "" # skip configure
    BUILD_COMMAND "" # skip build
    INSTALL_COMMAND "" # skip install
  )

endif()

set(BOOST_INCLUDE_DIRS ${EXTERNALS_DIR}/boost)
```

Add more boost subdirectories to boost download.
user
```cmake

if (DOWNLOAD_EXTERNALS)

  # Configure boost
  # ---------------
  # Note: a script is used to checkout a quasi minimal version
  set(DOWNLOAD_DIR ${EXTERNALS_DIR}/boost)

  ExternalProject_Add(boost
    DOWNLOAD_COMMAND svn co --depth files http://svn.boost.org/svn/boost/tags/release/Boost_1_50_0/boost
    DOWNLOAD_DIR ${DOWNLOAD_DIR}
    TMP_DIR ${DOWNLOAD_DIR}/tmp
    STAMP_DIR ${DOWNLOAD_DIR}/stamp
    UPDATE_COMMAND svn update
      ${DOWNLOAD_DIR}/boost/config
      ${DOWNLOAD_DIR}/boost/detail
      ${DOWNLOAD_DIR}/boost/exception
      ${DOWNLOAD_DIR}/boost/smart_ptr
      ${DOWNLOAD_DIR}/boost/algorithm
      ${DOWNLOAD_DIR}/boost/iterator
      ${DOWNLOAD_DIR}/boost/mpl
      ${DOWNLOAD_DIR}/boost/range
      ${DOWNLOAD_DIR}/boost/type_traits
      ${DOWNLOAD_DIR}/boost/preprocessor
      ${DOWNLOAD_DIR}/boost/utility
      ${DOWNLOAD_DIR}/boost/concept
      ${DOWNLOAD_DIR}/boost/function
      ${DOWNLOAD_DIR}/boost/bind
      ${DOWNLOAD_DIR}/boost/format
      ${DOWNLOAD_DIR}/boost/optional
      ${DOWNLOAD_DIR}
    CONFIGURE_COMMAND "" # skip configure
    BUILD_COMMAND "" # skip build
    INSTALL_COMMAND "" # skip install
  )

endif()

set(BOOST_INCLUDE_DIRS ${EXTERNALS_DIR}/boost)
```
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