## Changelog
Potentially breaking changes are marked with an exclamation point '!' at the begin of their description.
* 2017-??-?? v3.0.0
* Python wrapper now stable.
* ! REQUIRE macro now logs as error instead of fatal error.
* ! All macros and preprocessor defines now use the XERUS_ prefix. The config.mk file changed accordingly.
* ! TT::find_largest_entry and TT::dyadic_product left the TT scope.
* ! Tensor::modify_diag_elements renamed to Tensor::modify_diagonal_entries for naming consistency.
* Much faster solve of matrix equations Ax=b by exploiting symmetry and definiteness where possible. This directly speeds up the ALS as well.
* Added a highly optimized minimal version of the ALS algorithm as xALS.
* Added Tensor.one_norm() and one_norm(Tensor) to calculate the one norm of a Tensor.
* Some minor bugfixes and performance improvements.
* 2016-06-23 v2.4.0
* Introduced nomeclature 'mode'. Marked all functions that will be renamed / removed in v3.0.0 as deprecated.
* Added an experimental python wrapper when 'OTHER += -DXERUS_EXPERIMENTAL_PYTHON_WRAPPER' is defined in the config file.
* Added TT::degrees_of_freedom function to determine the dimension of the current tangent space.
* ! Corrected a typo in the class names of the measurement sets.
* Added constants xerus::VERSION_MAJOR, VERSION_MINOR, VERSION_REVISION and VERSION_COMMIT.
* Improved compilation time and more forgiving default settings for warnings.
* 2016-04-04 v2.3.0
* Added save_to_file and load_from_file functions to store and restore Tensors and TensorNetworks in/from files.
* Added SVD based calculate_pseudo_inverse function to Tensor.
* Added implementation for perform_trace() for sparse Tensors.
* Fixed the pipe operator for xerus::misc::generic_exception to not destroy the type information.
* Bug fix in the handling of fixed indices in TensorNetworks.
* Several static member function now warn if their return type is not used.
* Initial support for compilation with the intel ICC.
* 2016-03-11 v2.2.1
* Added support for 32bit systems.
* 2016-03-08 v2.2.0
* Added Sparse solve and sparse QR factorization.
* ! Xerus now depends on the SuiteSparseQR (-lspqr) library.
* TTNetwork sum now supports sparse components.
* TTNetwork entrywise\_product now supports sparse components.
* ! entrywise\_product (for TTNetworks) now a free function instead of static member.
* TTNetwork entrywise\_square now supports sparse components.
* Bugfix in Dense/Sparse conversion factor handling.
* 2016-02-10 v2.1.1
* Basic support for fixed indices in TensorNetworks.
* Readded TTNetwork constructor from DimensionTuple.
* Bugfixes for TTNetwork dyadic_product.
* 2016-02-05 v2.1.0
* ! fix_slate() now works correctly for TTTensors and (correctly) throws an error for TTOperators.
* Several bug fixes in the handling of TTNetworks of degree zero.
* Implemented the Tensor CQ function, which is now used where appropriate.
* Added several unit tests to ensure consitent results for dense/sparse Tensors, TensorNetwork and TTNetworks.
* Several Bugfixes in xerus::misc and a bugfix in TT:dyadic_product.
* 2016-01-26 v2.0.0
* ! Merged FullTensor and SparseTensor into a single Tensor class.
* Implemented several FullTensor functions also for sparse representations (modify(\_diag)_elements, fix\_slate, resize\_dimension,...)
* ! IndexedTensor*s now considered internal.
* ! Removed all support for stored IndexedTensor*s.
* ! Reworked the IndexedTensor* index assignment.
* ! Changed resize_dimension to allow slate insertion at the first position.
* Added TTTensor::random with callback function to manipulate the singular values of all matricisations.
* Rewrote the ALS algorithm for better readability.
* Added fully functional (multi-site) DMRG and alternating steepest descent algorithms.
* Support for low level factorisation calls for Tensor class.
* Several bug fixes, including SVD factor handling, SparseTensor summation, Tensor resize_dimension, TN evaluation,....
* Added several test cases.
* 2016-01-14 v1.5.0
* Added the ADF algorithm for rank one measurements instead of point evaluations.
* Parallelized the ADF algorithm using openmp (note: at this point not compatible with the replacement allocator!)
* TT::random no longer uses size_t to measure the size of the tensor and no longer exceeds maximal ranks.
* Fixed a bug in the ALS that caused the algorithm to always stop after one sweep if called without operator A.
* 2015-10-20 v1.4.2
* The custom allocator now enforces memory alignment even if the underlying malloc does not.
* Cannonicalized TT tensors can no longer exceed the maximal TT rank.
* 2015-10-14 v1.4.1
* Fixed a bug with the recannonicalization of products of TTOperators.
* Many improvements for the ADF algorithm for tensor completion.
* Added TTTensor::ones and TTOperator::ones to create TTTensors with all entries equal to 1.
* 2015-09-09 v1.4.0
* Added an implementation of the ADF algorithm.
* Added a custom allocator to better handle the small allocations of Indices etc. (requires to set the corresponding option in the config.mk).
* Reduced overhead (time not spent in blas) of TensorNetwork contractions.
* Tensor decomposition now allow arbitrary index orders in the target as well as the source.
* Added TN::measure(...) to perform a batch of evaluations of the network.
* Added TN::fix_slate(...) to fix a single index to a specific value.
* Added TN::reduce_representation() to trace out any full-rank edge.
* Added TN::transfer_core(...) and TN::round_edge(...) analogously to TT rounding / core movement operations.
* ! renamed class::construct_random to class::random and TTOperator::construct_identity to TTOperator::identity.
* Added several named constructors:
* Tensor::ones(...) to construct tensors filled with all entries equal to 1.
* Tensor::identity(...) to construct a (sparse) tensor equal to the TTOperator::identity.
* Tensor::dirac(...) to construct a (sparse) tensor with a single 1 at a given position and 0 everywhere else.
* Tensor::kronecker(...) to construct a tensor that is 1 when all indices are equal and 0 otherwise.
* ! misc::approx_equal now uses a relative difference (for consistency with the tensor variant xerus::approx_equal).
* Several bugfixes for SparseTensors.
* Several minor bugfixes (TN::draw no longer uses temporary files, span-zero indices in assignment, ...).
* 2015-07-10 v1.3.0
* Added several retractions to allow Riemannian algorithms on TT manifolds.
* Added the basic (Riemannian) steepest descent algorithm.
* Added the (so far untested) CG algorithm for TT tensors.
* ! New PerformanceData class to log stepcount, time and residual of algorithm runs.
* New algorithm to determine the largest entry of a TT tensor.
* Fully rewrote the contraction heuristics, now including a local search for more optimal contraction orders.
* Several bugfixes for order-zero tensors, TT tensors of more than full rank and other rare cases.
* 2015-06-15 v1.2.1
* entrywise_product for FullTensor and TTNetwork.
* TensorNetworks now without extraneous factor.
* 2015-06-15 v1.2.0
* Rank revealing QR decomposition in TTNetwork:move_core.
* ALS performance improvement by skipping full-rank nodes.
* Added TensorNetwork::draw to get a graphical representation of a given tensor network.
* Added algorithm DecompositionALS to approximate a FullTensor by a TTTensor.
* New Quick-Start guide.
* Several bugfixes, more consistent operator availability and much more documentation.
* 2015-06-02 v1.1.1
* Complete documentation for Tensor, FullTensor and SparseTensor
* Added implementation of the projection ALS
* Fixed performance bug in logging system
* ALS now uses energy functional for convergence testing
* Several minor fixes
* 2015-06-01 v1.1.0
* ! New representation for the TT tensors: all component tensors are now of degree 3 / 4 (operators).
* TT::get_component and ::set_component functions that handle the meta data.
* More strict ISO c++ conformity: no names starting with '__'.
* More elaborate performance profiling.
* 2015-05-27 v1.0.2
* Added support for Clang++
* ! Cleanup of namespace structure
* Several documentation fixes
* 2015-05-20 v1.0.1
* fixed a major bug with the handling of shared resources in TensorNetworks
* added TTTensor/TTOperator::chop() function
* some minor fixes
* 2015-05-19 v1.0
* first stable release