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## Changelog

#### Boost 1.89

- Update CMake minimum version and Python detection in CMake
- Improve documentation
  - Add example on how to make an axis which accepts multiple value types that are not implicitly convertible
  - Show how to use `histogram::fill` with a multidimensional histogram efficiently when data per dimension is already available as contiguous data
- Don't use deprecated form of user-defined literal operator
- Add support for modular build structure with b2
- Fixed warnings in MSVC about narrowed types
- Added collector accumulator, which stores all values in a bin
- Internal changes to tests and classes in detail namespace

#### Boost 1.88

- No changes.

#### Boost 1.87

- No changes.

#### Boost 1.86

- No changes.

#### Boost 1.85

- No changes.

#### Boost 1.84

- No changes.

#### Boost 1.83

- No changes.

#### Boost 1.82

- Replace `detail::span` and `detail::make_span` with implementations in `boost::core`
- Documentation improvements
- Protect usage of `std::min` and `std::max` in some cases, contributed by Han Jiang (min,max macros are illegially set by popular Windows headers so we need to work around)
- Added test to catch usage of unprotected min,max tokens in the library in the future
- Fixes to support latest clang-14 and deduction guides in gcc-11+

#### Boost 1.81

- Added new `accumulators::fraction` to compute fractions, their variance, and confidence intervals
- Added interval computers for fractions: `utility::clopper_pearson`, `utility::wilson_interval`, `utility::jeffreys_interval`, `utility::wald_interval` which can compute intervals with arbitrary confidence level
- Added `utility::confidence_level` and `utility::deviation` types to pass confidence levels as probabilities or in multiples of standard deviation for all interval computers, respectively
- Fixed internal `static_vector` and `span` in C++20

#### Boost 1.80

- Fixed segfault in `indexed` when trying to iterate over histogram with axes of zero size (physical or logical) under certain conditions
- Removed previously deprecated API:
  - class `accumulators::thread_safe`: use `accumulators::count<T, true>`
  - Methods `accumulators::sum::large` and `accumulators::sum::small`: use `accumulators::sum::large_part` and `accumulators::sum::small_part`
  - Type alias `algorithm::reduce_option`: use `algorithm::reduce_command`
  - Template function `axis::traits::static_options`: use `axis::traits::get_options`
  - Template function `axis::traits::static_is_inclusive`: use `axis::traits::is_inclusive`
  - Type alias `indexed::range_iterator`: use `indexed::iterator`
  - Type alias `indexed::accessor::reference`: use `indexed::accessor::const_reference`

#### Boost 1.79

- Division support for `accumulators::weighted_sum`
- `axis::regular` and `axis::variable` now represent closed intervals if overflow bin is absent, this is needed for example to correctly bin a probability in the closed interval [0, 1]
- cpp17 support: set axis compile-time options via deduction guide

#### Boost 1.78

- Deprecate `accumulators::sum::small` and `::large` as workaround for bug in windows.h
- Fixed broken division operator in `accumulators::count`
- Fix bug in 1D histogram::fill when axis is growing and argument is single value
- Improvements to documentation

#### Boost 1.77

- `indexed` now allows iteration over user-defined rectangular subrange
- Deprecate `accumulators::thread_safe`, users should replace with optionally thread-safe `accumulators::count`
- Fixed broken scaling operator in `accumulators::count`
- Fixed bug in `axis::integer::inclusive`
- Improvements to ostreaming: support for more accumulators, drawing unicode bar charts is now the default

#### Boost 1.76

- Fixes
  - `algorithm::reduce` with `crop` now does not remove the counts in flow bins anymore if the selected range actually overlaps with the flow bins, making the treatment of flow bins consistent with inner bins
  - `accumulators::mean` and `accumulators::weighted_mean` now compute the correct variance when `operator+=` was called, for example, when histograms with accumulators are added; this was wrong before leading to too small variances
  - detection of weight support in user-defined accumulators was broken at compile-time if accumulator used `operator+=` instead of `operator()`; tests only accidentally passed for builtin `weighted_sum`

#### Boost 1.75

- Fixes
  - `axis::variable{{0, 1, inf}}.value(1)` now returns 1 instead of NaN
  - `axis::variable` ctor now throws `std::invalid_argument` if one values is NaN
  - Implemented a workaround for a gcc bug (will be fixed upstream in gcc-10.x) that occurred when `<boost/type_traits.hpp>` was included before `<boost/histogram/axis/traits.hpp>`
  - Fixed several new warnings from the latest compiler versions
  - Fixed warnings that appear when compiling against the C++20 standard
- Documentation
  - Documented undefined behaviour when value and variance are requested for `accumulator::mean` and `accumulator::weighted_mean` but the accumulator does not have enough entries to compute them
  - Added explanation to rationale why axis metadata is checked for equality

#### Boost 1.74

- New features
  - New axis `boolean`, a special kind of integer axis with only two values and no state (except metadata)
  - Histograms with growing category axes are now addable even if the categories differ; the category axis of the output histogram is the union of the category axes of the input histograms
  - Added axis::traits::continuous to match axis::traits::is_continuous
- Fixes
  - `metadata()` method of builtin axis types now return a mutable reference even if the axis is const, as described in the documentation
- Documentation
  - Sorted headers in reference and sorted items in namespaces
  - Removed some internal typenames from templates
  - Added reference for `sample_type`
- Other
  - Simplified internal metaprogramming
  - Replaced Boost Assert with plain cassert

#### Boost 1.73

- New features
  - accumulators
    - New `count` accumulator, a thin wrapper around a primitive arithmetic type; serves as a base class for users who want to add arbitrary metadata to each bin
    - `sum` gained a `value()` method for consistency with other accumulators
  - algorithm
    - `reduce`
      - Now supports positional commands
      - `category` axis now supports `slice` command
      - Added `crop` command, like `shrink`, but discards content of removed bins
      - Renamed `reduce_option` to `reduce_command` (old name available but deprecated)
    - `sum` gained a new argument, allowing users to select whether to sum over all bins or only the inner bins (excluding underflow and overflow)
  - axis::traits
    - Added traits `is_ordered` and `ordered` to distinguish between different kinds of DiscreteAxis types; used internally to handle `category` axis and `integer` axis differently
    - Renamed `static_options` to `get_options` and `static_is_inclusive` to `is_inclusive` (old names available but deprecated)
- Fixes
  - Fixed failing ODR test in bundled Boost due to wrong paths
  - Fixed a bug in histogram::operator*= that could occur in user-defined accumulators
  - Fixed a bug in `indexed` which could cause arithmetic past the end position
  - Fixed a bug where the variance in `accumulators::weighted_sum` was not correctly computed if a normal histogram was added to the histogram that used `accumulators::weighted_sum`
  - Fixed a bug where compiling with `-ffast-math` would break `accumulators::sum`
  - Fixed `algorithm::reduce` to work with axes without *flow bins, which did not compile before
- Other
  - Added an example and documentation on how to use Boost.Histogram as a backend
  - Improved the docs on how to use custom accumulators and Boost.Accumulators
  - Many small documentation improvements
  - Improved docs for `algorithm::reduce`
  - Improved experimental cmake build support
  - Use `index_type` consistently everywhere instead of raw `int`
  - Benchmark update in the docs

#### Boost 1.72

- New features
  - Better deduction guides for axis types and histogram type on C++17 compilers
  - performance improvements in the indexing code
  - new histogram::fill method for accelerated filling from chunks of values
  - ASCII bar charts for 1D histograms when boost/histogram/ostream.hpp is included (contributed by Przemyslaw Bartosik)
  - Passing invalid axis options causes user-friendly compile-time errors
  - Wrong usage of weight() and sample() causes user-friendly compile-time errors
  - algorithm::empty returns true if all histogram values are equal to the default value (contributed by Henry Schreiner)
  - algorithm::reduce with shrink is now well defined when values are not bin edges
  - axis::traits::rank returns the number of values that this axis accepts
  - axis::traits::is_continuous returns whether an axis is continuous or discrete
  - axis::traits::is_inclusive returns whether an axis has a bin for any possible input
  - limited weight support for mean accumulator
  - accumulators::weighted_mean::sum_of_weights_squared method added
- Fixes
  - Support of -std=c++2a and -stdlib=libc++ on clang, compatibility with gcc-9
  - Fixed: weight could be passed instead of a sample during filling without triggering an error
  - Fixed: segfault when too many indices were passed to algorithm::project
  - Fixed: indexed range generator did not work with storage based on std::array
  - Fixed: weighted_mean() + weighted_mean() != weighted_mean() (discovered and reported by Henry Schreiner)
  - Fixed: axis::option::test(...) returned true if any bits in the test mask were set (now returns true if all bits in the test mask are set)
  - Protecting calls to min, max with against macro expansion
  - Replaced all crlf with lf in concepts.qbk
  - Missing throw of std::invalid_argument when user passes too many axes to histogram
  - Corrected documentation of serialization support in concepts section
  - Resolved warnings for various compiler versions
- Other
  - Added Boost.Histogram logo
  - Added missing copyright notices
  - axis::category::value returns copy for scalar types and const reference otherwise
  - std::ostringstream not used anymore to generate exception messages to reduces code bloat
  - Documentation improvements
    - Restructured overview section in documentation
    - Updated user guide to demonstrate new features
    - Updated accumulator examples
    - Concepts explain how accumulators can optionally accept weights
  - Updated benchmark code
  - New test checks consistency of b2 and cmake build systems
  - New test checks One-Definition-Rule (fails if non-templated function is not declared inline)
  - Serialization code decoupled from Boost.Serialization
  - Removed dependency on Boost.CallableTraits

#### Boost 1.71

- New features
  - Thread-safe accumulators boost::histogram::accumulators::thread_safe based on std::atomics
  - Support for thread-safe storages
  - Support for compiling without exceptions/RTTI (increases performance by 10-20 %) [with contributions from Glen Fernandez]
  - Performance improvements for 1D and 2D histograms
  - boost::histogram::indexed now returns forward iterator range instead of input iterator range
  - boost::histogram::indexed_range::accessor is now non-copyable and acts like reference to cell value, making most algorithms from the stdlib work
  - boost::histogram::algorithm::reduce
    - New slice option
    - Fuse shrink, slice, and rebin options passed for the same axis
    - Support histograms with some axis types with reduction support
  - boost::histogram::algorithm::project accepts runtime indices for static histograms
- Fixes
  - boost::histogram::algorithm::reduce also works on histograms that have some axis types without reduction support
  - boost::histogram::axis::traits::update now works correctly for boost::histogram::axis::variant
- Other
  - 100 % test coverage
  - Drastically reduced internal Boost dependencies
  - Improved documentation and examples
  - Internally replaced boost::variant with boost::variant2
  - boost::histogram::axis::traits::is_reducible detects reducible axis types
  - Cleanup and refactoring of internals
  - Guarantee no-throw moves for all builtin axis types
  - Improved internal benchmarks
  - Compile cleanly at higher warning levels

#### Boost 1.70

First Boost release, version 4.0 in former internal counting.

- Removed Python bindings, will be developed in separate repository
- All axes can be made optionally circular, except category axis
- All axes now support generic attached metadata
- All axes have now independently configurable underflow/overflow extra bins
- Removed circular axis (which is just a circular regular axis)
- Added indexed adaptor generator for convenient and fast iteration over histograms
- Support for axes that can grow in range
- Support for axes which accept multiple values (example: hexagonal binning)
- Support for profiles and more generally, arbitrary accumulators in each cell
- Support for serializing to xml archives
- Added compatibility with Boost.Range, Boost.Units, and Boost.Accumulators
- Added deduction guides for axis types and histogram
- Performance improvements
- Renamed `adaptive_storage` to `unlimited_storage`
- Replaced `boost::multiprecision::cpp_int` with custom type to decouple libraries
- Internal simplification of `axis::variant`
- Make all storages behave more like containers, simplifying the design
- Histograms supports add, sub, mul, div
- replaced `operator[]` in axis with explicit method `bin`
- replaced `operator()` in axis with explicit method `index`
- replaced internal use of `boost::containers` with stdlib containers
- Much improved docs, reference documentation, user guide, more examples

#### 3.2 (not in Boost)

- Allocator support everywhere
- Internal refactoring

#### 3.1 (not in Boost)

- Renamed `bincount` method to `size`
- Support for axes with only overflow and no underflow bin
- category axis now by default has bin for "other" input that does not fall into the predefined categories, making it consistent with other axes
- NaN is now consistently put into overflow bin for all axes
- Eliminated warnings about safe internal conversions on MSVC
- Established a cpp house style with corresponding .clang-format file
- Better detection of Python library on all systems
- Improved code coverage by testing more input errors
- Raise ValueError instead of generic RuntimeError in Python on input errors

#### 3.0 (not in Boost)

- Support for efficient adding of multiple histograms and scaling
- Re-design of category axis as a general mapping between unique values and bins
- Re-design of the bin description an axis returns upon element access
- Interface cleanup and simplification, more consistency between Python and C++ interface
- Iterators for histogram and axes for STL compatibility
- Regular axis in C++: Allowing transforms with state
- Regular axis in Python: Support for all C++ transforms
- Polymorphic axis::any type
- Internal refactoring from boost::mpl and boost::fusion to std::tuple and boost::mp11
- Windows support

#### 2.0 (not in Boost)

- Added static_histogram (v1.0 only had dynamic_histogram).
- Merged wfill(...) and fill(...) interface.
- Support custom allocators in storage classes.
- Replaced static_storage with array_storage.
- Replaced dynamic_storage with unlimited_storage, which adds the capability to grow the bin counter into a cpp_int, thus avoiding integer overflow completely.
- Serialization uses binary_archive instead of text_archive. The latter is portable, but the performance is terrible.
- Python interface changed: histograms are now iterable, returning axis classes
- Support reduction (removing a subset of axes and returning the equivalent histogram; in other words, those axes are integrated over)

#### 1.0 (not in Boost)

- First stable version.