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<title>Boost Basic Linear Algebra - Configuration Options</title>
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<body>
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<h1><img src="../../../../boost.png" align="middle" alt="logo"/>Boost Basic Linear Algebra - Configuration Options</h1>
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<div class="toc" id="toc"></div>
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<div class="navigation">
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<a href="index.html">back to uBLAS home</a>
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</div>
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<h2>NDEBUG</h2>
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<p><strong>Make sure you define NDEBUG</strong> The only way uBLAS
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knows you want a release configuration is to check if you have defined
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NDEBUG. If you don't it assumes you want a debug configuration and
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adds a lot of very useful runtime check. However these are very slow!
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</p>
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<h2>BOOST_UBLAS_MOVE_SEMANTICS</h2>
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<p class="credit">The patch and description was provided by Nasos Iliopoulos.</p>
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<p>An immediate effect of this option is the elimination of the need
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for noalias in types <tt>vector<T></tt> and <tt>matrix<T></tt>,
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when assigned to the same type. This option doesn't have an effect on
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bounded and c types. Although it is rare, not all compilers support copy
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elision (that allows for move semantics), so a test must be performed to
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make sure that there is a benefit when it is enabled. A small
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demonstration and test can be found in
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<a href="../test/manual/test_move_semantics.cpp"><tt>test_move_semantics.cpp</tt></a></p>
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<p>
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In the <a href="../test/manual/test_move_semantics.cpp">test
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example</a> two tests are defined, one for vectors and one for
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matrices. The aim of this example is to print the pointers of the
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storage of each of the containers, before and after the assignment to
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a temporary object. When move semantics are enabled, the
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<tt>vector<T></tt> and <tt>matrix<T></tt> storage is moved
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from the temporary and no copy is performed.
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</p>
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<p>
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If move semantics are supported by your compiler you will get an output like the following:
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</p>
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<pre class="screen">
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matrix<double> --------------------------------------------------------------------
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Temporary pointer r: 0x94790c0
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Pointer (must be equal to temp. pointer if move semantics are enabled) : 0x94790c0
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</pre>
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<p>Notes:</p>
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<ul>
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<li>It should be no surprise to see matrices and vectors been passed
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by VALUE, the compiler takes care and either moves (if the underlying
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code does not modify the object), or copies (if the underlying code
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modifies the object).
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</li>
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<li>There might be some space for some improvements (like clearing the
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data, before swaping)
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</li>
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<li>Move semantics don't eliminate temporaries. They rather move their
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storage around so no copies are performed.
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</li>
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<li>MSVC does no implement Named Return Value Optimization in debug
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mode. So if you build in debug with this compiler you might get <a
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href="https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=483229"
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target="_blank">different behaviour</a> than a release build.
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</li>
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<li>Enabling move semantics is done via #define BOOST_UBLAS_MOVE_SEMANTICS.
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</li>
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<li>There is plenty of room for optimizations when c++0x standard is
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out, taking advantage of rvalue references. (I have a sweet vector
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implementation using that).
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</li>
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<li>If you enable move semantics and your compiler does not support
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them, the operation will just be as passing by const reference.
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</li>
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</ul>
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<p>Interesting links</p>
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<ul>
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<li> <a href="http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/" target="_blank">Want Speed? Pass by Value.</a>
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</li>
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<li> <a href="http://blogs.msdn.com/vcblog/archive/2009/02/03/rvalue-references-c-0x-features-in-vc10-part-2.aspx" target="_blank">Rvalue References: C++0x Features in VC10, Part 2</a>
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</li>
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<li> <a href="http://cpp-next.com/archive/2009/09/move-it-with-rvalue-references/" target="_blank">Move It With Rvalue References</a>
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</li>
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</ul>
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<h2>BOOST_UBLAS_CHECK_ENABLE</h2>
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<p>When BOOST_UBLAS_CHECK_ENABLE is defined then all index and
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parameter checks are enabled. This is enabled in debug mode and
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disabled in release mode.
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</p>
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<h2>BOOST_UBLAS_TYPE_CHECK</h2>
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<p>When BOOST_UBLAS_TYPE_CHECK is enabled then all possibly expensive
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structure checks are enabled. If this is not desireable then use
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<tt>#define BOOST_UBLAS_TYPE_CHECK 0</tt> before including any uBLAS
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header. The define BOOST_UBLAS_TYPE_CHECK_EPSILON can be used to
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control the acceptable tolerance, see
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<tt>detail/matrix_assign.hpp</tt> for implementation details of this
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check.
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</p>
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<h2>BOOST_UBLAS_USE_LONG_DOUBLE</h2>
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<p>Enable uBLAS expressions that involve containers of 'long double'</p>
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<h2>BOOST_UBLAS_USE_INTERVAL</h2>
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<p>Enable uBLAS expressions that involve containers of 'boost::numeric::interval' types</p>
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<h2>Configuring uBLAS with Macros</h2>
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<p>Many macro's appear in ublas/config.hpp and elsewhere. Hopefully in the future some of these will disappear!
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They fall into 4 groups:
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</p>
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<ul>
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<li> Automatically set by 'boost/numeric/ublas/config.hpp' based on
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NDEBUG. Makes the distinction between debug (safe) and release (fast)
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mode. Similar to STLport
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<ul>
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<li> <i>Release</i> mode (NDEBUG defined)
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<ul>
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<li> BOOST_UBLAS_INLINE <i>Compiler dependant definition to control
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function inlining.</i> </li><li> BOOST_UBLAS_USE_FAST_SAME </li></ul>
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</li><li> <i>Debug</i> mode
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<ul>
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<li> BOOST_UBLAS_CHECK_ENABLE <i>Enable checking of indexs, iterators
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and parameters. Prevents out of bound access etc.</i> </li><li>
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BOOST_UBLAS_TYPE_CHECK <i>Enable additional checks for the results of
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expressions using non dense types. Picks up runtime error such as the
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assignment of a numerically non-symmetric matrix to
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symmertic_matrix. Use <tt>#define BOOST_UBLAS_TYPE_CHECK 0</tt> to
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disable expensive numeric type checks.</i> (Note: "structure check"
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would be a much better name.) </li><li>
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BOOST_UBLAS_TYPE_CHECK_EPSILON <i>default: sqrt(epsilon), controls how
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large the difference between the expected result and the computed
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result may become. Increase this value if you are going to use near
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singular or badly scaled matrices. Please, refer to
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<tt>detail/matrix_assign.hpp</tt> for implementation of these type
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checks.</i> </li></ul> </li></ul>
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</li>
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<li> Automatically set by 'boost/numeric/ublas/config.hpp' based on
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compiler and boost/config.hpp macro's. Augments the compiler
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deficiency workarounds already supplied by boost/config.hpp
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<ul>
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<li> BOOST_UBLAS_NO_NESTED_CLASS_RELATION <i>A particularly nasty
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problem with VC7.1 Requires that uBLAS and the user use begin(it)
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rather then it.begin()</i> </li><li> BOOST_UBLAS_NO_SMART_PROXIES
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<i>Disable the automatic propagation of 'constantness' to
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proxies. Smart proxies automatically determine if the underling
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container they reference is constant or not. They adjust there
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definition of iterators and container access to reflect this
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constantness.</i> </li></ul>
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</li>
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<li> For use by uBLAS authors to test implementation methods. Preset
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in config.hpp
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<ul>
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<li> BOOST_UBLAS_USE_INVARIANT_HOISTING </li><li>
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BOOST_UBLAS_USE_INDEXING </li><li> BOOST_UBLAS_USE_INDEXED_ITERATOR
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</li><li> BOOST_UBLAS_NON_CONFORMANT_PROXIES <i>Gappy containers may
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be non-conformant, that is contain elements at different
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indices. Assigning between proxies (vector ranges for example) of
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these containers is difficult as the LHS may need insert new
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elements. This is slow.</i> </li><li> BOOST_UBLAS_USE_DUFF_DEVICE
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<i>Near useless on all platforms (see GCC's -funroll-loops)</i>
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</li></ul>
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</li>
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<li> User options. Can be predefined by user before including any
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uBLAS headers. They may also be automatically defined for some
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compilers to work around compile bugs.
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<ul>
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<li> BOOST_UBLAS_USE_LONG_DOUBLE <i>Enable uBLAS expressions that
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involve containers of 'long double'</i> </li><li>
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BOOST_UBLAS_USE_INTERVAL <i>Enable uBLAS expressions that involve
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containers of 'boost::numeric::interval' types</i> </li><li>
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BOOST_UBLAS_SIMPLE_ET_DEBUG <i>In order to simplify debugging is is
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possible to simplify expression templateso they are restricted to a
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single operation</i>
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</li><li> BOOST_UBLAS_ENABLE_PROXY_SHORTCUTS <i> enable automatic
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conversion from proxy class to matrix expression </i> </li><li>
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BOOST_UBLAS_NO_ELEMENT_PROXIES <i>Disables the use of element proxies
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for gappy types.</i> </li><li> <i>The Gappy types (sparse, coordinate,
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compressed) store non-zero elements in their own containers. When new
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non-zero elements are assigned they must rearrange these
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containers. This invalidates references, iterators or pointers to
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these elements. This can happen at some surprising times such as the
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expression "a [1] = a [0] = 1;". Element proxies guarantee all such
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expressions will work as expected. However they bring their own
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restrictions and efficiency problems. For example as of Boost 1.30.0
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they prevent the assignment of elements between different types.</i>
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</li>
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<li> BOOST_UBLAS_REFERENCE_CONST_MEMBER <i>Enable to allow refernces
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to be returned to fixed (zero or one) elements of triangular or banded
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matrices</i>
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</li><li> BOOST_UBLAS_NO_EXCEPTIONS <i>Disable the use exceptions of
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uBLAS internal checks and error conditions. BOOST_NO_EXCEPTIONS has
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same effect.</i>
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</li>
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<li> BOOST_UBLAS_SINGULAR_CHECK <i>Check the for singularity in triangular solve() functions</i></li>
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</ul>
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</li>
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</ul>
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<hr />
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<div id="copyright">
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<p>Copyright (©) 2000-2009 Joerg Walter, Mathias Koch, Gunter Winkler<br />
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Use, modification and distribution are subject to the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">
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http://www.boost.org/LICENSE_1_0.txt
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</a>).
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</p>
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</div>
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<div id="revision">
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<p>
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<!-- Created: Wed Sep 16 21:19:20 CEST 2009 -->
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<!-- hhmts start -->
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Last modified: Wed Sep 16 23:16:45 CEST 2009
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<!-- hhmts end -->
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