RELEASE-NOTES.txt

STANC3 RELEASE NOTES
======================================================================

v2.35.0 (3 June 2024)
======================================================================

 - Rename `sampling statement (~)` to `distribution statement (~)` to be consistent with the docs changes. (#1426)
 - The generated C++ no longer assumes that the RNG used in Stan is specifically the `boost::ecuyer1988` generator, but uses a type alias defined in the Stan library. (#1395)
 - Fixed an issue where multiple `reject` statements could cause the C++ compiler to fail. (#1396)
 - Giving a variable the name `jacobian` is now deprecated. This name is being reserved for future language extensions. (#1397)
 - When encountering an unknown identifier that matches a known suffixed function without its suffix, add the known function name to the error message. (#1401)
 - Added `fatal_error()`, which is similar to `reject()` but rather than signaling an error which is recoverable, signals an error which should terminate execution immediately. `fatal_error` is now a reserved word. (#1402)
 - Exposed the new overloads of `wiener_lpdf` added to Stan Math by @Franzi2114. (#1411)
 - Added a better error message when a program attempts to use the removed array syntax. (#1413)
 - Use tabs to position error message cursor when appropriate. (#1414)
 - Replaced the link show when the deprecated `lkj_cov` distribution is used with the new link (see https://github.com/stan-dev/docs/pull/694). (#1415)
 - The compiler should display a cleaner error if it encounters an internal error. (#1416)
 - Clarified the error messages generated by a syntax error on the right side of an assignment statement. (#1417)
 - Removed code following the last round of syntax deprecations that is currently scheduled. The final one (use of `real` values in conditionals) is now a type error and can no longer be automatically canonicalized. (#1420)
 - Fixed an issue where `operator/` was not generating the correct C++ for complex linear algebra types. (#1421)
 - Rollback js_of_ocaml to 5.4.0 for compatibility with QuickJS. (#1427) 

v2.34.0 (16 January 2024)
======================================================================

- Added the `binomial_logit_glm` distribution (#1367)
- Added the `dirichlet_multinomial` distribution. (#1389)
- Added the ability to unpack a tuple during an assignment. For example, the following is now valid:
    ```stan
    parameters {
    matrix[N, M] A;
    }
    model {
    matrix[N, M] Q;
    matrix[M, M] R;
    (Q, R) = qr_thin(A); // qr_thin returns a tuple(matrix, matrix)
    }
    ```
    (#1360)
- Exposed vectorized signatures for the `atan2` function. (#1364)
- The Stan compiler will now warn you when you reassign a variable to itself. (#1358)
- Updated the OCaml-to-JS compiler used to create stanc.js (#1365, #1381)
- Updated the compiler to use OCaml 4.14 and newer versions of its dependencies. (#1366)
- Reverted a change to SoA initialization, as the Math library has implemented a better fix. (#1376)
- Fixed an issue with clang compilers and constructing tuples. (#1382)
- The compiler no longer recognizes language constructs removed in 2.33. (#1388)
- The deprecated implicit conversion of reals to boolean conditions has been removed. (#1388)

v2.33.1 (13 September 2023)
======================================================================

- Fixed several issues with the code generation of user-defined functions which accepted tuples (#1356)

v2.33.0 (5 September 2023)
======================================================================

- Added tuple types to the language (#1100)
- The following deprecations have been turned into errors this version:
    - The old array syntax, e.g. `int arr[5];`. Use `array[5] int arr;` instead.
    - Distribution functions ending in `_log`. Use either `_lpdf` or `_lpmf`.
    - The functions `binomial_coefficient_log`, `multiply_log`, and `cov_exp_quad`. Use `lchoose`, `lmultiply`, and `gp_exp_quad_cov` respectively.
    - The `if_else` function. Use the ternary operator  `cond ? true_value : false_value`
    - Use of CDFs with a `,` between the first and second argument. Use a `|`.
    - Comments beginning with `#`. Use `//`.
    - Use of `<-` for assignment. Use `=`.
    - The `increment_log_prob` function. Use the `target +=` statement.
    - The `get_lp()` function. Use `target()`.
    - The use of nested multi-indices on the left hand side of an assignment statement.
    For this version, these can all be automatically updated with the `--canonicalize=deprecations` argument to the autoformatter. This is not guaranteed to work for versions _following_ this one.
    Additionally, the following identifiers are now reserved words: `array`, `offset`, `multiplier`, `lower`, and `upper`.
    (#1287)
- Exposed vectorized signatures for `log_sum_exp` (#1344)
- Exposed new functions `qr`, `qr_thin`,  `eigendecompose_sym`, `eigendecompose`, `complex_schur_decompose`, `svd`, and `csr_extract`. (#1346)
- Added a `log_prob_impl` specialization specifically for reverse mode to improve code generation (#1327)
- Fixed an issue where returning array literals could produce the wrong types in C++. (#1335)
- Fixed an issue with leading zeroes in real literals like `0E0` (#1336)
- Fixed a bug with type promotion in the arguments to user-defined distributions generating bad C++. (#1338)
- Fixed optimization logic for deducing whether mixes of scalars, data matrices, and autodiff matrices can be promoted to SoA (#1347)
- Fixed an issue with the partial evaluator crashing on statements containing a mod-by-zero. (#1351)
- `--filename-in-msg` now also affects the name of the file shown in runtime exceptions. Useful for interfaces which use mangled or temporary names during compilation. (#1339)
- Improved error message provided when the wrong return type is returned from a function.
    Return statements now follow the same type promotion rules as assignment and function argument passing.
    The typechecker now allows infinite loops (`while (1)` without an internal `break`) to be the end of a returning function. Previously, an (unreachable) return statement was needed following the loop.
    (#1341)
- Improved error messages for unsupported type in reduce_sum (#1332)
- Improved error messages when using a reserved word as a variable name. (#1343)

v2.32.1 (2 May 2023)
======================================================================

- The shapes and sizes of parameter initial values are now checked against the specified sizes in the model before being read in, matching the existing behavior for data. (#1316)
  **Note:** This change may cause existing code which worked "by accident" to raise new errors about mismatches between the model's declarations and the provided initialization.
- Errors in transform_inits should now properly highlight the location in the original Stan program. (#1318)
- Fixed an issue where the `--debug-generate-inits` debug flag would fail badly if parameter sizes depended on data (#1319)

v2.32.0 (20 April 2023)
======================================================================

- Syntax removals scheduled for this version have been pushed back to 2.33. We still recommend updating your Stan models as you are able. As a reminder, deprecated syntax which will be removed in minor versions can as a rule be updated automatically using find-and-replace tools or the [Stan compiler's auto-formatting abilities](https://mc-stan.org/docs/stan-users-guide/stanc-pretty-printing.html). (#1303)
- The deprecated `--include_paths` and `--allow_undefined` arguments have been removed, use `--include-paths` and `--allow-undefined`. (#1303)
- Recursive user-defined functions no longer need forward declarations. (#1277)
- Added overloads to `eigenvalues` and `eigenvectors` which accept a complex matrix as input. (#1282)
- Fixed an issue where `profile` blocks could generate uncompilable C++ when used with `--O1`. (#1281)
- Fixed an issue where the compiler would generate uncompilable C++ when a matrix expression featured mixed types of elements. (#1292)
- Fixed an issue where a user-defined-function expecting real arguments could be passed an integer and exhibit integer behavior like truncating division. (#1296)
- Fixed an issue where external functions could not be used in higher-order functions without the end-user supplying an implementation of our functor structs. (#1298)
- Fixed a bug in `transform_inits` for models which used complex types (#1305)
- Improved the error shown when an `#include`d file cannot be found to list the paths it searched on. (#1273)
- Improved `--filename-in-msg` for the command line version of `stanc`. Errors now use the requested name, not just warnings. (#1274)
- Refactored how C++ is code-generated in the compiler. (#1233)
- Added tests for various parts of the C++ backend which weren't previously tested, and added a `--debug-lir` flag to print out the C++ representation in a s-expression. (#1276)
- Updated code generate of `get_param_names` (#1245)
- Switched to `std::endl` instead of `'\n'` to end prints. (#1301)
- Added a new function `unconstrain_array` to the generated code. This is currently not exposed. (#1305)
- Added a `--debug-generate-inits` flag to stanc which behaves like `--debug-generate-data` but for declarations in the `parameters` block. (#1306)
- Sped up some code which is critical to parsing. (#1302)

v2.31.0 (21 November 2022)
======================================================================

- Improved the error message for bad multiple declarations. (#1239)
- Fixed a bug where using a C++ reserved word as a name in certain situations would prevent compilation. (#1243)
- Build binaries in parallel on Jenkins. (#1244)
- Added functions `complex_schur_decompose_t()` and `complex_schur_decompose_u()` implementing the complex-valued Schur decomposition for matrices.(#1247)
- Vectorized the `conj` function for complex types.(#1253)
- CI change, build backwards-compatible Mac executables on flatiron mac. (#1255)
- Improved the error generated when a function is re-declared, or when a function is not given a definition. (#1256)
- `print` and `reject` will now be listed as functions in `stanc --info`s output. (#1257)
- Added quantile functions (inverse-CDFs) `std_normal_qf` and `std_normal_log_qf`. `std_normal_qf` is a synonym for `inv_Phi`, and `std_normal_log_qf` is the same but with the input on the log-scale.(#1258)
- Fix using `reject()` with container types. (#1261)
- Vectorized sampling statements can now be used with the truncation syntax `T[ , ]`(#1263)
- Functions which return integer types are considered as "data" for purposes of data-only arguments.(#1265)
- The negation operator `-` can now accept arrays, e.g. `array[N] int foo = {...}; print(-foo);`(#1266)
- Exposes algebraic functions with a variadic arguments, using the following four functions: `solve_powell`, `solve_powell_tol`, `solve_newton` and `solve_newton_tol`.  Relevant changes to Stan-math are already merged.(#1268)

v2.30.1 (27 July 2022)
======================================================================

- Improved the pedantic mode warning for parameters without priors. The message now highlights when it is safe to ignore it.
- Fixed a bug in the memory pattern optimization where a for loop generated for the function inliner would prevent detection of for loops higher in the control flow graph.
- Fixed an issue with the function inliner when a function local variable had the same name as a variable in the calling scope.
- Fixed an issue where recursive functions which called themselves with a slice of their arguments would lead to infinite template expansion in C++ compilation.
- Fixed a bug in stanc.js where the stanc flags were not listed correctly in the generated C++.
- The imaginary components of complex vectors and matrices are now initialized to NaN to match the real component and behaviour of non-complex vectors and matrices.

v2.30.0 (1 July 2022)
======================================================================

Complex:
 - Added complex containers: `complex_matrix`, `complex_vector`, and `complex_row_vector` with basic arithmetic support. (#1133)
 - Fixed indexing of a complex container to return the correct type. (#1158)
 - Added many common linear algebra functions and container operations for complex types. (#1166)
 - Fixed an issue reading in `complex_matrix` in the data block. (#1168)
 - Added vectorized signatures for `get_real` and `get_imag`, e.g. `get_real(complex_matrix) => matrix`. (#1169)
 - Added `fft`, `inv_fft`, `fft2`, and `inv_fft2` to the language. (#1170)
 - `pow` (and subsequently the `^` operator) now have overloads for complex containers. (#1186)
 - `to_complex` is now vectorized. This means signatures like `to_complex(matrix, matrix) => complex_matrix` are now available. (#1208)
 - Added signatures for addition, subtraction and division which mix scalars and complex vector types, broadcasting the scalar as appropriate. (#1212)
 - Added `svd_U`, `svd_V`, `singular_values`, `eigenvalues_sym`, and `eigenvectors_sym` for complex inputs. (#1212)

New functions:
 - Added `L1` and `L2` norms. (#1140)
 - Added `log_determinant_spd` which is faster when the input matrix is known to be symmetric and positive definite. (#1178)
 - Added `wishart_cholesky_lpdf` and `wishart_cholesky_rng` distribution functions. (#1188)
 - Added `multi_student_t_cholesky_lpdf` and `multi_student_t_cholesky_rng` distribution functions. (#1197)
 - Added `inv_wishart_cholesky_lpdf` and `inv_wishart_cholesky_rng` distribution functions. (#1202)
 - Exposes inv_inc_beta. (#1211)

Misc:
 - Re-enabled function inlining optimizations at O1. (#1097)
 - Modified the optimizer to turn statements like `3 + 4i` into `to_complex(3,4)` directly. (#1112)
 - Added `cumulative_sum(Vector/RowVector)` for `var<Matrix>` types. (#1152)
 - Improved compile times by accumulating all template requirements into a single `require_all_t` on user defined functions. (#1157)
 - The `--info` and `--debug-generate-data` commands now use the Yojson library for it's output. (#1161, #1175)
 - Bugfixed for output values in `write_array` that should be `NaN`. (#1165)
 - `--dump-stan-math-signatures` now prints an entire signature on one line, no matter how long it is. (#1167)
 - Fix --debug-generate-data for ordered vector data types. (#1173)
 - Exposed an overload for `cumulative_sum` which takes and returns an array of integers. (#1174)
 - The javascript interface (stancjs) now generates errors which look more like stanc3's by pointing out where in the supplied code the error occurred. (#1177)
 - Cleaned up the internal structuring of modules in the compiler. (#1179)
 - Cleaned up code for pretty printing the Middle Intermediate Representation (MIR). (#1180)
 - Added `--debug-mem-patterns` flag, which will print out the memory type of variables (either Array of Structs or the more efficient Struct of Arrays pattern) when optimization is enabled. (#1185)
 - Allowed the adding of new distributions without requiring them to support deprecated suffixes. (#1191)
 - Added `eigenvectors` and `eigenvalues` functions which return the complex-valued eigenvectors or eigenvalues of a real (asymmetrix) matrix. (#1192)
 - `abs` is now vectorized for container types. `fabs` is now deprecated, as all usages can be replaced with `abs` thanks to array promotion rules. (#1195)
 - Made installing the developer tools for the Stanc repository an interactive script with error handling. (#1200)
 - Internally clean up how variable declarations are represented. (#1203)
 - Simplified internal representations in the compiler. (#1204)
 - The pretty-printer now preserves multiple declarations in one line like `int a, b;` rather than splitting them into two declarations. (#1207)
 - Declarations are now allowed in places they previously would not parse, such as the only statement in the body of an if statement. (#1207)
 - `./`, `/` `.*`, and `*` now have consistent behavior with scalar arguments. (#1209)

v2.29.2 (25 March 2022)
======================================================================

- Fixed a bug fix with `--O1` when arrays declared in transformed parameters or model were assigned data.
- Added missing signatures for `normal_id_glm_lpdf`.
- Fixed a compilation error with forward declarations.
- Disabled AD level optimizations in `--O1` optimizations.
- MIR pretty printing now always adds ( and ) around the ternary operator ?:

v2.29.1 (2 March 2022)
======================================================================

- Formatting without a | when only one argument is supplied to a distribution.
- Stanc previously would allow you to erroneously assign a function to a different functions name using =, which then failed in C++ compilation. This is now an error.
- Nonlinear transforms of the LHS of a tilde statement now produce warnings in pedantic mode.
- Improved type error messages for operators and tilde statements.

v2.29.0 (14 February 2022)
======================================================================

FEATURES
 - Allow most reserved words in C++ (e.g., `public`) to appear in a stan program; they will be changed by the compiler to `_stan_<reserved word>` in the generated C++. (#962)
 - User defined functions can now be overloaded. Multiple definitions of the same function name are allowed if the arguments are different in each definition.(#1027)
 - Improved error messages for incorrect variable declarations. (#1099)
 - When an unknown identifier is encountered Stan will suggest nearby known names you might have meant (#1024)
 - Extra semicolons in `data` or `parameters` no longer produce syntax errors. (#988)
 - Improved error messages for incomplete probability library calls. (#1021)
 - Added nicer error message when a comment is unterminated at end of input. (#1025)
 - All internal compiler errors now include a link to the stanc3 issues page. (#1028)
 - Improve error messages when a user tries to declare a function argument as a constrained type. (#1030)
 - Replaced the use of the word twiddle with tilde in pedantic warning messages. (#1050)
 - Allow user-defined densities over complex arguments and deeply nested arguments. (#1046)
 - Added optimization layers `--O0` (default), `--O1`, and `--Oexperimental`
 - Turn back on allowing immediately assigned to decls not be NaN initialized at `O1` (#1029)
 - Allows `log_prob_impl` to use Struct of Arrays type for reverse mode autodiff at `O1` (#955)
 - Issue a warning when a user has a model with unreachable statements, such as code following a `return` statement. (#1063)
 - The compiler can now compile or format standalone function definitions in a `.stanfunctions` file. These are compiled as if a normal Stan program was compiled with `stanc3 --standalone-functions` and can be used with `#include` statements in the `functions` block (#1022)
 - The canonicalizer can now have each part enabled seperately. This can be done with commands like `stanc --auto-format --canonicalize=braces,deprecations <model>`. Current options are `deprecations`, `braces`, and `parenthesis`. (#1058)
 - Ensure the canonicalizer properly prints nested if-else statements. (#1055)
 - `--auto-format` no longer prints code which originated from an `#include` directive. This can be re-enabled by using `canonicalize=includes`. (#1069)
 - When using `--auto-format`, the user can now pass `--max-line-length=#` to set the column number at which the formatter will try to break lines. (#1068)
 - Tweak pretty-printing of if-else blocks. (#1008)
 - Canonicalizer now adds brackets around single statements in if-else/for/while. (#1003)
 - Expose `bernoulli_logit_glm_rng` functions. (#1034)
 - lchoose now has the same signatures as binomial_coefficient_log. (#1010)
 - Added `ordered_probit_lpmf(array[] int, real, vector) => real` and `ordered_probit_lpmf(array[] int, real, array[] vector) => real`. (#1073)
 - Added additional `normal_id_glm` signatures. (#1084)
 - Added signatures for `inv_erfc` function. (#1090)
 - Added Differential-Algebraic Equation solver (`dae`, `dae_tol`). (#1092)
 - Added `von_mises_cdf`, `von_mises_lcdf`, von_mises_lccdf`. (#1085)
 - Added `loglogistic_lpdf`, `loglogistic_log`, `loglogistic_rng` and `loglogistic_cdf`. (#1094)
 - Clean up more mutable state in the Javascript interface (#1118)

DEPRECATIONS
 - Added a warning for `matrix^scalar` that points users to `.^` and `matrix_power()`. (#1026)
 - Warn about the following identifiers being reserved in a future version: `array`, `upper`, `lower`, `offset`, `multiplier`. (#1048)
 - The old form of declaring arrays like `real a[5]`, which has been deprecated since 2.26, now issues a warning. (#1072)
 - Marked existing syntax deprecations (e.g., `<-`) as expiring in Stan 2.32.0. (#1044)
 - Deprecate nested multi-indexing on lvalues as it is inconsistent with rvalues.(#1059)

BUGFIXES
 - Fixed an issue that arose during C++ compilation of models that used a variable with the same name as a Stan library function and called that function. (#1011)
 - Fixed a bug where the lexer was allowing illegal variable names which began with an underscore. (#962)
 - Fixed an issue with parser errors 'sticking around' on subsequent runs, which primarily affected the Javascript compiler. (#1074)

DEVELOPER
 - Updated OCaml and build dependencies. (#1019)
 - Create internal developer documentation at https://mc-stan.org/stanc3/stanc/. (#1006)
 - stan2tfp now lives in a seperate repo at stan-dev/stan2tfp. (#1040)
 - Refactored Stan typechecker. (#995)
 - Replaces all references to Docker Hub for andrjohns images with stanorg. (#1017)
 - Move docker to ci-scripts repository. (#1020)
 - Refactored when logic for binaries builds and release. (#1018)
 - Added optimization level flags, debug-* and dump-math-signatures flags to stancjs. (#1082)
 - Compile Tests and Model end-to-end tests run now optionally only when test/integration/good has changed. (#1018)

v2.28.1 (21 October 2021)
======================================================================

- Expose missing arg() function
- Turned off default of allow_uninitialized_decls
- Fixed transform_inits input and output sizes

Note: There are known issues during compilation when calling functions that expect complex arguments with variables of type `int` or `real`.
If this is required, please wrap the arguments with a call to `to_complex()`. This will be addressed in the next release.

v2.28.0 (5 October 2021)
======================================================================

- Int division is now handled by the Warnings module to print this to stderr and to avoid printing to stderr directly (a problem for stanc.js). (#869)
- Correct canonicalizing/auto-formatting of commented Stan programs; comments no longer discarded. (#894)
- Improved error messages when argument types don't match the function signature. (#907)
- A warning is now produced if an empty file is compiled. (#919)
- Stancjs now has `--info` and `--debug-generate-data` options.(#920)
- Added support for `skew_double_exponential` distribution.(#921)
- Reorganized warning system internally.(#922)
- Removed initialization of NA values from objects that are immediately assigned to(#930)
- Added `to_matrix(array[] row_vector) => matrix`. (#931)
- Added build process for arm64, armhf, armel, mips64el, ppc64el and s390x linux architectures. (#936)
- Implemented complex type functionality. (#940)
- Added types used for deducing memory patterns. (#944)
- Removes dune runtest from binary build stage. (#950)
- Provide rough support for non-ASCII characters in string literals. (#952)
- Clean up internal exception handling. (#957)
- Added the ability to write imaginary numbers as literals, such as "3.1i". (#963)
- Added a list of included files to the information provided by `--info`. (#965)
- Tweaked pretty-printing of conditional distribution applications. (#967)
- Better pretty-printing for long constraints. (#970)
- Fix automated builds of non-x86 architectures. (#972)
- Fixed a bug with the conditional operator `?` and the use of vector or matrix expressions. (#977)
- Fixed a typo in the error message displayed when a file cannot be found. (#981)
- Error messages should now always have a trailing newline. (#982)
- Miscellaneous README.md improvements. (#914, #943, #984)

v2.27.0 (2 June 2021)
======================================================================

 - Added the `--info` argument to output a list of functions and distributions used.(#813)
 - Added `ode_ckrk` and `ode_ckrk_tol` to the Stan language.(#828)
 - Cleaned up indexing by using variadic rvalue and assign functions.(#829)
 - Fixed incorrect codegen for mixed-type array expressions.(#830)
 - Added building ARM to our infrastructure.(#832, #833)
 - Made locations_array constexpr and moved curr_statement__ to function scope.(#842, #845)
 - Added range checks.(#849, #521)
 - Consolidated the use of | in cdf functions to match lpdf/lpmf and lccdf functions. Comma version of cdf function is deprecated.(#863)
 - Adds signatures for data-only quantile functions.(#870)
 - Cleanup readability of the C++.(#871)
 - Adds vectorized versions of `fma()`.(#888)
 - Fixed optimizer crash on divide-by-zero expressions.(#891)
 - Added clearing of read/write events for global matrix_cls.(#897)
 - Added  `ode_adjoint_tol_ctl` and improved type printing with variadic ODEs.(#900)

v2.26.1 (15 February 2021)
======================================================================

- Fixed issue with not allowing user-defined _lp functions with a void return type in transformed parameters block.

v2.26.0 (26 January 2021)
======================================================================

 - Added deprecated functions warnings to regular use, and replace in canonicalizer.(#726)
 - Added a small readme for dockerfiles usage locally.(#738)
 - Added `matrix chol2inv(matrix)`.(#740)
 - Added a Github Actions job to build binaries.(#747)
 - Modified code-generation for user-defined functions to accept Eigen expressions.(#752)
 - Added OpenCL support for: bernoulli_lpmf, bernoulli_logit_lpmf, beta_lpdf, beta_proportion_lpdf, binomial_lpmf, cauchy_lpdf, chi_square_lpdf, double_exponential_lpdf, exp_mod_normal_lpdf, exponential_lpdf, frechet_lpdf, gamma_lpdf, gumbel_lpdf, inv_chi_square_lpdf, inv_gamma_lpdf, logistic_lpdf, lognormal_lpdf, neg_binomial_lpmf, neg_binomial_2_lpmf, neg_binomial_2_log_lpmf, normal_lpdf, pareto_lpdf, pareto_type_2_lpdf, poisson_lpmf, poisson_log_lpmf, rayleigh_lpdf, scaled_inv_chi_square_lpdf, skew_normal_lpdf, std_normal_lpdf, student_t_lpdf, uniform_lpdf, weibull_lpdf
 - Allowed `write_array()`, `log_prob()`, and `transform_inits()` to avoid a vector copy and read/write(#761)
 - Added the discrete_range distribution.(#763)
 - Use Eigen comma initializer to avoid copy in vector construction.(#766)
 - Allowed calling lp functions in transformed parameters block.(#767)
 - Fixed multi-dim indexing bug.(#768)
 - Moved the reported location of parsing errors closer to the problematic section.(#771)
 - Fixed a optimization bug in handling of unnormalized distributions.(#778)
 - Added profiling to the Stan language.(#794)
 - Added `linspaced_int_array()`(#796)

v2.25.0 (26 October 2020)
======================================================================

- Improved parser error message on missing semicolon in the data or parameters block.
- Expanded OpenCL (GPU) support for GLMs to now handle parameters for any argument.
- Fix parameter unconstraining bug when the constraints depend on other constrained parameters.
- "offset, "multiplier," "lower," and "upper" are no longer reserved keywords and can be used in the names of identifiers.
- Extended `elt_multiply` (`.*`) and `elt_divide` (`./`) to cases where both inputs are scalars.
- Added support for unnormalized distributions for the `target +=` sytnax.
- Changed the MIR to represent function declarations as Options.
- Variable names are now allowed that shadow math function names.
- Fixed a bug with not recognizing transformed parameters in pedantic mode
- Added vectorised binary functions:
    - bessel_first_kind
    - beta
    - binary_log_loss
    - binomial_coefficient_log
    - choose
    - falling_factorial
    - fdim
    - fmax
    - fmin
    - fmod
    - gamma_p
    - gamma_q
    - hypot
    - lbeta
    - ldexp
    - lmgamma
    - log_diff_exp
    - log_falling_factorial
    - log_inv_logit_diff
    - log_modified_bessel_first_kind
    - log_rising_factorial
    - modified_bessel_first_kind
    - modified_bessel_second_kind
    - lmultiply
    - multiply_log
    - owens_t
    - rising_factorial

Code contributions were made by @andrjohns @nhuurre @rok-cesnovar @rybern and @seantalts

v2.24.1 (11 August 2020)
======================================================================

Bugfixes:

- added using std::pow to generated code
- fixed code generation for pow()
- added data quantifier to linspaced_* signatures
- fixed code generation for empty matrices

v2.24.0 (28 July 2020)
======================================================================

New functions:
   `algebra_solver_newton`

   `matrix hmm_hidden_state_prob(matrix, matrix, vector)`
   `int[] hmm_latent_rng(matrix, matrix, vector)`
   `real hmm_marginal(matrix, matrix, vector)`

   `T lambert_w0(T)`, for any T
   `T lambert_w1(T)`, for any T

   `matrix matrix_power(matrix, int)`

   `real multinomial_logit_log(int[], vector)`
   `real multinomial_logit_lpmf(int[], vector)`
   `int[] multinomial_logit_rng(vector, int)`

   `ode_adams`, `ode_adams_tol`
   `ode_bdf`, `ode_bdf_tol`
   `ode_rk45`, `ode_rk45_tol`

   `T pow(int, T)`
   `T pow(real, T)`
   `T pow(T, int)`
   `T pow(T, real) `
    (previously only real pow(real, real) was available)

   `T reverse(T)`, where T is vector, row_vector or an array of any type

   `matrix identity_matrix(int)`
   `real[] linspaced_array(int, real, real); row_vector linspaced_row_vector(int, real, real); vector linspaced_vector(int, real, real)`
   `int[] one_hot_int_array(int, int); real[] one_hot_array(int, int); row_vector one_hot_row_vector(int, int); vector one_hot_vector(int, int)`
   `int[] ones_int_array(int); real[] ones_array(int); row_vector ones_row_vector(int); vector ones_vector(int)`
   `vector uniform_simplex(int)`
   `int[] zeros_int_array(int); real[] zeros_array(int); row_vector zeros_row_vector(int); vector zeros_vector(int)`


New features:

- pedantic mode
- experimental optimization mode
- new integer division operator `%/%`
- non-scalar values are now allowed in lower, upper, offset and multiplier
- integrate_ode_* functions are now deprecated
- data-only restricted functions now work with parameters in generated quantities
- improved out-of-bounds messages for vectors, matrices
- added checks for invalid literals
- `--allow_undefined` and `--include_paths` are deprecated in favor of `--allow-undefined` and `--include-paths`
- cleaned up the generated model C++ code: model is now final, using statements instead of typedef, better use of inline, use of `.clear()` instead of `.resize(0)`, remove unnecessary functions
- cleaned up the OCaml code: better use of helper functions, removed duplicate functions, better exception messages, replace imperative code for handling Stan Math signatures
- size expressions for parameters and generated quantities are now only evaluated once
- better handle model names that are not C++ friendly (start with numbers, have non-alphanumeric characters)

Bugfixes:
- changed the loop index type to int to prevent issues when using it in expressions with signed numbers
- integer arrays now initialize to the smallest representable integer
- var arrays initialize with a prebuilt dummy var, to not creat new varis
- all map_rect calls are registered when using MPI
- _lpdf/_lpmf functions are now used instead of *_log when generating code for the tilde statements
- single argument distribution do not require the vertical bar anymore (e.g. std_normal_lpdf(x|))
- fixed a bug that caused tilde statements to conflict with userdef functions
- rng functions are no longer allowed in size declarations
- fixed the _lpdf functor struct so that UDF with _log and int argument now compile
- fixed array literal type-checking
- fixed the error messages for missing input (line number is now displayed properly)
- fixed indexing in transform_init()
- fixed emitting generated quantities only (for gq_writer)
- fixed debug data generator for constrained matrix types and added array value bounds