switching to high quality piper tts and added label translations

2026-01-29 23:48:19 +01:00
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+#
+# sympy.polys.matrices.linsolve module
+#
+# This module defines the _linsolve function which is the internal workhorse
+# used by linsolve. This computes the solution of a system of linear equations
+# using the SDM sparse matrix implementation in sympy.polys.matrices.sdm. This
+# is a replacement for solve_lin_sys in sympy.polys.solvers which is
+# inefficient for large sparse systems due to the use of a PolyRing with many
+# generators:
+#
+#     https://github.com/sympy/sympy/issues/20857
+#
+# The implementation of _linsolve here handles:
+#
+# - Extracting the coefficients from the Expr/Eq input equations.
+# - Constructing a domain and converting the coefficients to
+#   that domain.
+# - Using the SDM.rref, SDM.nullspace etc methods to generate the full
+#   solution working with arithmetic only in the domain of the coefficients.
+#
+# The routines here are particularly designed to be efficient for large sparse
+# systems of linear equations although as well as dense systems. It is
+# possible that for some small dense systems solve_lin_sys which uses the
+# dense matrix implementation DDM will be more efficient. With smaller systems
+# though the bulk of the time is spent just preprocessing the inputs and the
+# relative time spent in rref is too small to be noticeable.
+#
+
+from collections import defaultdict
+
+from sympy.core.add import Add
+from sympy.core.mul import Mul
+from sympy.core.singleton import S
+
+from sympy.polys.constructor import construct_domain
+from sympy.polys.solvers import PolyNonlinearError
+
+from .sdm import (
+    SDM,
+    sdm_irref,
+    sdm_particular_from_rref,
+    sdm_nullspace_from_rref
+)
+
+from sympy.utilities.misc import filldedent
+
+
+def _linsolve(eqs, syms):
+
+    """Solve a linear system of equations.
+
+    Examples
+    ========
+
+    Solve a linear system with a unique solution:
+
+    >>> from sympy import symbols, Eq
+    >>> from sympy.polys.matrices.linsolve import _linsolve
+    >>> x, y = symbols('x, y')
+    >>> eqs = [Eq(x + y, 1), Eq(x - y, 2)]
+    >>> _linsolve(eqs, [x, y])
+    {x: 3/2, y: -1/2}
+
+    In the case of underdetermined systems the solution will be expressed in
+    terms of the unknown symbols that are unconstrained:
+
+    >>> _linsolve([Eq(x + y, 0)], [x, y])
+    {x: -y, y: y}
+
+    """
+    # Number of unknowns (columns in the non-augmented matrix)
+    nsyms = len(syms)
+
+    # Convert to sparse augmented matrix (len(eqs) x (nsyms+1))
+    eqsdict, const = _linear_eq_to_dict(eqs, syms)
+    Aaug = sympy_dict_to_dm(eqsdict, const, syms)
+    K = Aaug.domain
+
+    # sdm_irref has issues with float matrices. This uses the ddm_rref()
+    # function. When sdm_rref() can handle float matrices reasonably this
+    # should be removed...
+    if K.is_RealField or K.is_ComplexField:
+        Aaug = Aaug.to_ddm().rref()[0].to_sdm()
+
+    # Compute reduced-row echelon form (RREF)
+    Arref, pivots, nzcols = sdm_irref(Aaug)
+
+    # No solution:
+    if pivots and pivots[-1] == nsyms:
+        return None
+
+    # Particular solution for non-homogeneous system:
+    P = sdm_particular_from_rref(Arref, nsyms+1, pivots)
+
+    # Nullspace - general solution to homogeneous system
+    # Note: using nsyms not nsyms+1 to ignore last column
+    V, nonpivots = sdm_nullspace_from_rref(Arref, K.one, nsyms, pivots, nzcols)
+
+    # Collect together terms from particular and nullspace:
+    sol = defaultdict(list)
+    for i, v in P.items():
+        sol[syms[i]].append(K.to_sympy(v))
+    for npi, Vi in zip(nonpivots, V):
+        sym = syms[npi]
+        for i, v in Vi.items():
+            sol[syms[i]].append(sym * K.to_sympy(v))
+
+    # Use a single call to Add for each term:
+    sol = {s: Add(*terms) for s, terms in sol.items()}
+
+    # Fill in the zeros:
+    zero = S.Zero
+    for s in set(syms) - set(sol):
+        sol[s] = zero
+
+    # All done!
+    return sol
+
+
+def sympy_dict_to_dm(eqs_coeffs, eqs_rhs, syms):
+    """Convert a system of dict equations to a sparse augmented matrix"""
+    elems = set(eqs_rhs).union(*(e.values() for e in eqs_coeffs))
+    K, elems_K = construct_domain(elems, field=True, extension=True)
+    elem_map = dict(zip(elems, elems_K))
+    neqs = len(eqs_coeffs)
+    nsyms = len(syms)
+    sym2index = dict(zip(syms, range(nsyms)))
+    eqsdict = []
+    for eq, rhs in zip(eqs_coeffs, eqs_rhs):
+        eqdict = {sym2index[s]: elem_map[c] for s, c in eq.items()}
+        if rhs:
+            eqdict[nsyms] = -elem_map[rhs]
+        if eqdict:
+            eqsdict.append(eqdict)
+    sdm_aug = SDM(enumerate(eqsdict), (neqs, nsyms + 1), K)
+    return sdm_aug
+
+
+def _linear_eq_to_dict(eqs, syms):
+    """Convert a system Expr/Eq equations into dict form, returning
+    the coefficient dictionaries and a list of syms-independent terms
+    from each expression in ``eqs```.
+
+    Examples
+    ========
+
+    >>> from sympy.polys.matrices.linsolve import _linear_eq_to_dict
+    >>> from sympy.abc import x
+    >>> _linear_eq_to_dict([2*x + 3], {x})
+    ([{x: 2}], [3])
+    """
+    coeffs = []
+    ind = []
+    symset = set(syms)
+    for e in eqs:
+        if e.is_Equality:
+            coeff, terms = _lin_eq2dict(e.lhs, symset)
+            cR, tR = _lin_eq2dict(e.rhs, symset)
+            # there were no nonlinear errors so now
+            # cancellation is allowed
+            coeff -= cR
+            for k, v in tR.items():
+                if k in terms:
+                    terms[k] -= v
+                else:
+                    terms[k] = -v
+            # don't store coefficients of 0, however
+            terms = {k: v for k, v in terms.items() if v}
+            c, d = coeff, terms
+        else:
+            c, d = _lin_eq2dict(e, symset)
+        coeffs.append(d)
+        ind.append(c)
+    return coeffs, ind
+
+
+def _lin_eq2dict(a, symset):
+    """return (c, d) where c is the sym-independent part of ``a`` and
+    ``d`` is an efficiently calculated dictionary mapping symbols to
+    their coefficients. A PolyNonlinearError is raised if non-linearity
+    is detected.
+
+    The values in the dictionary will be non-zero.
+
+    Examples
+    ========
+
+    >>> from sympy.polys.matrices.linsolve import _lin_eq2dict
+    >>> from sympy.abc import x, y
+    >>> _lin_eq2dict(x + 2*y + 3, {x, y})
+    (3, {x: 1, y: 2})
+    """
+    if a in symset:
+        return S.Zero, {a: S.One}
+    elif a.is_Add:
+        terms_list = defaultdict(list)
+        coeff_list = []
+        for ai in a.args:
+            ci, ti = _lin_eq2dict(ai, symset)
+            coeff_list.append(ci)
+            for mij, cij in ti.items():
+                terms_list[mij].append(cij)
+        coeff = Add(*coeff_list)
+        terms = {sym: Add(*coeffs) for sym, coeffs in terms_list.items()}
+        return coeff, terms
+    elif a.is_Mul:
+        terms = terms_coeff = None
+        coeff_list = []
+        for ai in a.args:
+            ci, ti = _lin_eq2dict(ai, symset)
+            if not ti:
+                coeff_list.append(ci)
+            elif terms is None:
+                terms = ti
+                terms_coeff = ci
+            else:
+                # since ti is not null and we already have
+                # a term, this is a cross term
+                raise PolyNonlinearError(filldedent('''
+                    nonlinear cross-term: %s''' % a))
+        coeff = Mul._from_args(coeff_list)
+        if terms is None:
+            return coeff, {}
+        else:
+            terms = {sym: coeff * c for sym, c in terms.items()}
+            return  coeff * terms_coeff, terms
+    elif not a.has_xfree(symset):
+        return a, {}
+    else:
+        raise PolyNonlinearError('nonlinear term: %s' % a)