.. _mpoly:

**mpoly.h** -- support functions for multivariate polynomials
===============================================================================

    An array of type ``ulong *`` or ``fmpz **`` is used to communicate
    exponent vectors. These exponent vectors must have length equal to the
    number of variables in the polynomial ring.
    The element of this exponent vector at index `0`
    corresponds to the most significant variable in the monomial ordering.
    For example, if the polynomial is `7\cdot x^2\cdot y+8\cdot y\cdot z+9` and the variables are
    ordered so that `x>y>z`, the degree function will return `\{2,1,1\}`.
    Similarly, the exponent vector of the `0`-index term of this polynomial is
    `\{2,1,0\}`, while the `2`-index term has exponent vector `\{0,0,0\}` and
    coefficient `9`.



Orderings
--------------------------------------------------------------------------------
.. type:: ordering_t

     An enumeration of supported term orderings.  Currently one of ``ORD_LEX``, 
     ``ORD_DEGLEX`` or ``ORD_DEGREVLEX``.

.. type:: mpoly_ctx_struct
          mpoly_ctx_t

     An mpoly_ctx_struct is a structure holding information about the number of
     variables and the term ordering of a multivariate polynomial.

.. function:: void mpoly_ctx_init(mpoly_ctx_t ctx, slong nvars, const ordering_t ord)

    Initialize a context for specified number of variables and ordering.

.. function:: void mpoly_ctx_clear(mpoly_ctx_t mctx)

    Clean up any space used by a context object.

.. function:: ordering_t mpoly_ordering_randtest(flint_rand_t state)

    Return a random ordering. The possibilities are ``ORD_LEX``,
    ``ORD_DEGLEX`` and ``ORD_DEGREVLEX``.

.. function:: void mpoly_ctx_init_rand(mpoly_ctx_t mctx, flint_rand_t state, slong max_nvars)

    Initialize a context with a random choice for the ordering.

.. function:: int mpoly_ordering_isdeg(const mpoly_ctx_t ctx)

    Return 1 if the ordering of the given context is a degree ordering (deglex or degrevlex).

.. function:: int mpoly_ordering_isrev(const mpoly_ctx_t cth)

    Return 1 if the ordering of the given context is a reverse ordering (currently only
    degrevlex).

.. function:: void mpoly_ordering_print(ordering_t ord)

    Print a string (either "lex", "deglex" or "degrevlex") to standard
    output, corresponding to the given ordering.


Monomial arithmetic
--------------------------------------------------------------------------------


.. function:: void mpoly_monomial_add(ulong * exp_ptr, const ulong * exp2, const ulong * exp3, slong N)

    Set ``(exp_ptr, N)`` to the sum of the monomials ``(exp2, N)`` and
    ``(exp3, N)``, assuming ``bits <= FLINT_BITS``

.. function:: void mpoly_monomial_add_mp(ulong * exp_ptr, const ulong * exp2, const ulong * exp3, slong N)

    Set ``(exp_ptr, N)`` to the sum of the monomials ``(exp2, N)`` and
    ``(exp3, N)``.

.. function:: void mpoly_monomial_sub(ulong * exp_ptr, const ulong * exp2, const ulong * exp3, slong N)

    Set ``(exp_ptr, N)`` to the difference of the monomials ``(exp2, N)`` and ``(exp3, N)``, assuming ``bits <= FLINT_BITS``

.. function:: void mpoly_monomial_sub_mp(ulong * exp_ptr, const ulong * exp2, const ulong * exp3, slong N)

    Set ``(exp_ptr, N)`` to the difference of the monomials ``(exp2, N)`` and ``(exp3, N)``.

.. function:: int mpoly_monomial_overflows(ulong * exp2, slong N, ulong mask)

    Return true if any of the fields of the given monomial ``(exp2, N)`` has
    overflowed (or is negative). The ``mask`` is a word with the high bit of
    each field set to 1. In other words, the function returns 1 if any word of
    ``exp2`` has any of the nonzero bits in ``mask`` set. Assumes that
    ``bits <= FLINT_BITS``.

.. function:: int mpoly_monomial_overflows_mp(ulong * exp_ptr, slong N, flint_bitcnt_t bits)

    Return true if any of the fields of the given monomial ``(exp_ptr, N)``
    has overflowed. Assumes that ``bits >= FLINT_BITS``.

.. function:: int mpoly_monomial_overflows1(ulong exp, ulong mask)

    As per ``mpoly_monomial_overflows`` with ``N = 1``.

.. function:: void mpoly_monomial_set(ulong * exp2, const ulong * exp3, slong N)

    Set the monomial ``(exp2, N)`` to ``(exp3, N)``.

.. function:: void mpoly_monomial_swap(ulong * exp2, ulong * exp3, slong N)

    Swap the words in ``(exp2, N)`` and ``(exp3, N)``.

.. function:: void mpoly_monomial_mul_ui(ulong * exp2, const ulong * exp3, slong N, ulong c)

    Set the words of ``(exp2, N)`` to the words of ``(exp3, N)``
    multiplied by ``c``.


Monomial comparison
--------------------------------------------------------------------------------


.. function:: int mpoly_monomial_is_zero(const ulong * exp, slong N)

    Return 1 if ``(exp, N)`` is zero.

.. function:: int mpoly_monomial_equal(const ulong * exp2, const ulong * exp3, slong N)

    Return 1 if the monomials ``(exp2, N)`` and ``(exp3, N)`` are equal.

.. function:: void mpoly_get_cmpmask(ulong * cmpmask, slong N, ulong bits, const mpoly_ctx_t mctx)

    Get the mask ``(cmpmask, N)`` for comparisons.
    ``bits`` should be set to the number of bits in the exponents
    to be compared. Any function that compares monomials should use this
    comparison mask.

.. function:: int mpoly_monomial_lt(const ulong * exp2, const ulong * exp3, slong N, const ulong * cmpmask)

    Return 1 if ``(exp2, N)`` is less than ``(exp3, N)``.

.. function:: int mpoly_monomial_gt(const ulong * exp2, const ulong * exp3, slong N, const ulong * cmpmask)

    Return 1 if ``(exp2, N)`` is greater than ``(exp3, N)``.

.. function:: int mpoly_monomial_cmp(const ulong * exp2, const ulong * exp3, slong N, const ulong * cmpmask)

    Return `1` if ``(exp2, N)`` is greater than, `0` if it is equal to and
    `-1` if it is less than ``(exp3, N)``.


Monomial divisibility
--------------------------------------------------------------------------------


.. function:: int mpoly_monomial_divides(ulong * exp_ptr, const ulong * exp2, const ulong * exp3, slong N, ulong mask)

    Return 1 if the monomial ``(exp3, N)`` divides ``(exp2, N)``. If so
    set ``(exp_ptr, N)`` to the quotient monomial. The ``mask`` is a word
    with the high bit of each bit field set to 1. Assumes that
    ``bits <= FLINT_BITS``.

.. function:: int mpoly_monomial_divides_mp(ulong * exp_ptr, const ulong * exp2, const ulong * exp3, slong N, flint_bitcnt_t bits)

    Return 1 if the monomial ``(exp3, N)`` divides ``(exp2, N)``. If so
    set ``(exp_ptr, N)`` to the quotient monomial. Assumes that
    ``bits >= FLINT_BITS``.

.. function:: int mpoly_monomial_divides1(ulong * exp_ptr, const ulong exp2, const ulong exp3, ulong mask)

    As per ``mpoly_monomial_divides`` with ``N = 1``.


.. function:: int mpoly_monomial_divides_tight(slong e1, slong e2, slong * prods, slong num)

    Return 1 if the monomial ``e2`` divides the monomial ``e1``, where
    the monomials are stored using factorial representation. The array
    ``(prods, num)`` should consist of `1`, `b_1, b_1\times b_2, \ldots`,
    where the `b_i` are the bases of the factorial number representation.


Basic manipulation
--------------------------------------------------------------------------------


.. function:: flint_bitcnt_t mpoly_exp_bits_required_ui(const ulong * user_exp, const mpoly_ctx_t mctx)

    Returns the number of bits required to store ``user_exp`` in packed
    format. The returned number of bits includes space for a zeroed signed bit.

.. function:: flint_bitcnt_t mpoly_exp_bits_required_ffmpz(const fmpz * user_exp, const mpoly_ctx_t mctx)

    Returns the number of bits required to store ``user_exp`` in packed
    format. The returned number of bits includes space for a zeroed signed bit.

.. function:: flint_bitcnt_t mpoly_exp_bits_required_pfmpz(fmpz * const * user_exp, const mpoly_ctx_t mctx)

    Returns the number of bits required to store ``user_exp`` in packed
    format. The returned number of bits includes space for a zeroed signed bit.
    
.. function:: void mpoly_max_fields_ui_sp(ulong * max_fields, const ulong * poly_exps, slong len, ulong bits, const mpoly_ctx_t mctx)

    Compute the field-wise maximum of packed exponents from ``poly_exps``
    of length ``len`` and unpack the result into ``max_fields``.
    The maximums are assumed to fit a ulong.

.. function:: void mpoly_max_fields_fmpz(fmpz * max_fields, const ulong * poly_exps, slong len, ulong bits, const mpoly_ctx_t mctx)

    Compute the field-wise maximum of packed exponents from ``poly_exps``
    of length ``len`` and unpack the result into ``max_fields``.

.. function:: void mpoly_max_degrees_tight(slong * max_exp, ulong * exps, slong len, slong * prods, slong num)

    Return an array of ``num`` integers corresponding to the maximum degrees
    of the exponents in the array of exponent vectors ``(exps, len)``,
    assuming that the exponent are packed in a factorial representation. The
    array ``(prods, num)`` should consist of `1`, `b_1`,
    `b_1\times b_2, \ldots`, where the `b_i` are the bases of the factorial
    number representation. The results are stored in the array ``max_exp``,
    with the entry corresponding to the most significant base of the factorial
    representation first in the array.

.. function:: int mpoly_monomial_exists(slong * index, const ulong * poly_exps, const ulong * exp, slong len, slong N, const ulong * cmpmask)

    Returns true if the given exponent vector ``exp`` exists in the array of
    exponent vectors ``(poly_exps, len)``, otherwise, returns false. If the
    exponent vector is found, its index into the array of exponent vectors is
    returned. Otherwise, ``index`` is set to the index where this exponent
    could be inserted to preserve the ordering. The index can be in the range
    ``[0, len]``.

.. function:: void mpoly_search_monomials(slong ** e_ind, ulong * e, slong * e_score, slong * t1, slong * t2, slong *t3, slong lower, slong upper, const ulong * a, slong a_len, const ulong * b, slong b_len, slong N, const ulong * cmpmask)

    Given packed exponent vectors ``a`` and ``b``, compute a packed
    exponent ``e`` such that the number of monomials in the cross product
    ``a`` X ``b`` that are less than or equal to ``e`` is between
    ``lower`` and ``upper``. This number is stored in ``e_store``. If
    no such monomial exists, one is chosen so that the number of monomials is as
    close as possible. This function assumes that ``1`` is the smallest
    monomial and needs three arrays ``t1``, ``t2``, and ``t3`` of the
    size as ``a`` for workspace. The parameter ``e_ind`` is set to one
    of ``t1``, ``t2``, and ``t3`` and gives the locations of the
    monomials in ``a`` X ``b``.


Setting and getting monomials
--------------------------------------------------------------------------------


.. function:: int mpoly_term_exp_fits_ui(ulong * exps, ulong bits, slong n, const mpoly_ctx_t mctx)

    Return whether every entry of the exponent vector of index `n` in
    ``exps`` fits into a ``ulong``.

.. function:: int mpoly_term_exp_fits_si(ulong * exps, ulong bits, slong n, const mpoly_ctx_t mctx)

    Return whether every entry of the exponent vector of index `n` in
    ``exps`` fits into a ``slong``.

.. function:: void mpoly_get_monomial_ui(ulong * exps, const ulong * poly_exps, ulong bits, const mpoly_ctx_t mctx)

    Convert the packed exponent ``poly_exps`` of bit count ``bits`` to a
    monomial from the user's perspective. The exponents are assumed to fit
    a ulong.

.. function:: void mpoly_get_monomial_ffmpz(fmpz * exps, const ulong * poly_exps, flint_bitcnt_t bits, const mpoly_ctx_t mctx)

    Convert the packed exponent ``poly_exps`` of bit count ``bits`` to a
    monomial from the user's perspective.

.. function:: void mpoly_get_monomial_pfmpz(fmpz ** exps, const ulong * poly_exps, flint_bitcnt_t bits, const mpoly_ctx_t mctx)

    Convert the packed exponent ``poly_exps`` of bit count ``bits`` to a
    monomial from the user's perspective.

.. function:: void mpoly_set_monomial_ui(ulong * exp1, const ulong * exp2, ulong bits, const mpoly_ctx_t mctx)

    Convert the user monomial ``exp2`` to packed format using ``bits``.

.. function:: void mpoly_set_monomial_ffmpz(ulong * exp1, const fmpz * exp2, flint_bitcnt_t bits, const mpoly_ctx_t mctx)

    Convert the user monomial ``exp2`` to packed format using ``bits``.

.. function:: void mpoly_set_monomial_pfmpz(ulong * exp1, fmpz * const * exp2, flint_bitcnt_t bits, const mpoly_ctx_t mctx)

    Convert the user monomial ``exp2`` to packed format using ``bits``.


Packing and unpacking monomials
--------------------------------------------------------------------------------


.. function:: void mpoly_pack_vec_ui(ulong * exp1, const ulong * exp2, ulong bits, slong nfields, slong len)

    Packs a vector ``exp2`` into \{exp1} using a bit count of ``bits``.
    No checking is done to ensure that the vector actually fits
    into ``bits`` bits. The number of fields in each vector is
    ``nfields`` and the total number of vectors to unpack is ``len``.
    

.. function:: void mpoly_pack_vec_fmpz(ulong * exp1, const fmpz * exp2, flint_bitcnt_t bits, slong nfields, slong len)

    Packs a vector ``exp2`` into \{exp1} using a bit count of ``bits``.
    No checking is done to ensure that the vector actually fits
    into ``bits`` bits. The number of fields in each vector is
    ``nfields`` and the total number of vectors to unpack is ``len``.

.. function:: void mpoly_unpack_vec_ui(ulong * exp1, const ulong * exp2, ulong bits, slong nfields, slong len)

    Unpacks vector ``exp2`` of bit count ``bits`` into ``exp1``.
    The number of fields in each vector is
    ``nfields`` and the total number of vectors to unpack is ``len``.

.. function:: void mpoly_unpack_vec_fmpz(fmpz * exp1, const ulong * exp2, flint_bitcnt_t bits, slong nfields, slong len)

    Unpacks vector ``exp2`` of bit count ``bits`` into ``exp1``.
    The number of fields in each vector is
    ``nfields`` and the total number of vectors to unpack is ``len``.

.. function:: int mpoly_repack_monomials(ulong * exps1, ulong bits1, const ulong * exps2, ulong bits2, slong len, const mpoly_ctx_t mctx)

    Convert an array of length ``len`` of exponents ``exps2`` packed
    using bits ``bits2`` into an array ``exps1`` using bits ``bits1``.
    No checking is done to ensure that the result fits into bits ``bits1``.
 
.. function:: void mpoly_pack_monomials_tight(ulong * exp1, const ulong * exp2, slong len, const slong * mults, slong num, slong bits)

    Given an array of possibly packed exponent vectors ``exp2`` of length
    ``len``, where each field of each exponent vector is packed into the
    given number of bits, return the corresponding array of monomial vectors
    packed using a factorial numbering scheme. The "bases" for the factorial
    numbering scheme are given as an array of integers ``mults``, the first
    entry of which corresponds to the field of least significance in each 
    input exponent vector. Obviously the maximum exponent to be packed must be
    less than the corresponding base in ``mults``.

    The number of multipliers is given by ``num``. The code only considers
    least significant ``num`` fields of each exponent vectors and ignores
    the rest. The number of ignored fields should be passed in ``extras``.

.. function:: void mpoly_unpack_monomials_tight(ulong * e1, ulong * e2, slong len, slong * mults, slong num, slong bits)

    Given an array of exponent vectors ``e2`` of length ``len`` packed
    using a factorial numbering scheme, unpack the monomials into an array
    ``e1`` of exponent vectors in standard packed format, where each field
    has the given number of bits. The "bases" for the factorial
    numbering scheme are given as an array of integers ``mults``, the first
    entry of which corresponds to the field of least significance in each 
    exponent vector.
  
    The number of multipliers is given by ``num``. The code only considers
    least significant ``num`` fields of each exponent vectors and ignores the
    rest. The number of ignored fields should be passed in ``extras``.


Chunking
--------------------------------------------------------------------------------


.. function:: void mpoly_main_variable_terms1(slong * i1, slong * n1, const ulong * exp1, slong l1, slong len1, slong k, slong num, slong bits)

    Given an array of exponent vectors ``(exp1, len1)``, each exponent
    vector taking one word of space, with each exponent being packed into the
    given number of bits, compute ``l1`` starting offsets ``i1`` and
    lengths ``n1`` (which may be zero) to break the exponents into chunks.
    Each chunk consists of exponents have the same degree in the main variable.
    The index of the main variable is given by `k`. The variables are indexed
    from the variable of least significance, starting from `0`. The value 
    ``l1`` should be the degree in the main variable, plus one.


Chained heap functions
--------------------------------------------------------------------------------


.. function:: int _mpoly_heap_insert(mpoly_heap_s * heap, ulong * exp, void * x, slong * next_loc, slong * heap_len, slong N, const ulong * cmpmask)

    Given a heap, insert a new node `x` corresponding to the given exponent
    into the heap. Heap elements are ordered by the exponent ``(exp, N)``,
    with the largest element at the head of the heap. A pointer to the current
    heap length must be passed in via ``heap_len``. This will be updated by
    the function. Note that the index 0 position in the heap is not used, so
    the length is always one greater than the number of elements.

.. function:: void _mpoly_heap_insert1(mpoly_heap1_s * heap, ulong exp, void * x, slong * next_loc, slong * heap_len, ulong maskhi)

    As per ``_mpoly_heap_insert`` except that ``N = 1``, and 
    ``maskhi = cmpmask[0]``.

.. function:: void * _mpoly_heap_pop(mpoly_heap_s * heap, slong * heap_len, slong N, const ulong * cmpmask)

    Pop the head of the heap. It is cast to a ``void *``. A pointer to the
    current heap length must be passed in via ``heap_len``. This will be
    updated by the function. Note that the index 0 position in the heap is not
    used, so the length is always one greater than the number of elements. The 
    ``maskhi`` and ``masklo`` values are zero except for degrevlex
    ordering, where they are as per the monomial comparison operations above.

.. function:: void * _mpoly_heap_pop1(mpoly_heap1_s * heap, slong * heap_len, ulong maskhi)

    As per ``_mpoly_heap_pop1`` except that ``N = 1``, and 
    ``maskhi = cmpmask[0]``.

