Source code for sympy.solvers.solveset

"""
This module contains functions to:

- solve a single equation for a single variable, in any domain either real or complex.

- solve a system of linear equations with N variables and M equations.
"""
from __future__ import print_function, division

from sympy.core.sympify import sympify
from sympy.core import S, Pow, Dummy, pi, Expr, Wild, Mul, Equality
from sympy.core.numbers import I, Number, Rational, oo
from sympy.core.function import (Lambda, expand, expand_complex)
from sympy.core.relational import Eq
from sympy.simplify.simplify import simplify, fraction, trigsimp
from sympy.core.symbol import Symbol
from sympy.functions import (log, Abs, tan, cot, sin, cos, sec, csc, exp,
acos, asin, acsc, asec, arg,
piecewise_fold)
from sympy.functions.elementary.trigonometric import (TrigonometricFunction,
HyperbolicFunction)
from sympy.functions.elementary.miscellaneous import real_root
from sympy.sets import (FiniteSet, EmptySet, imageset, Interval, Intersection,
Union, ConditionSet)
from sympy.matrices import Matrix
from sympy.polys import (roots, Poly, degree, together, PolynomialError,
RootOf)
from sympy.solvers.solvers import checksol, denoms, unrad
from sympy.solvers.inequalities import solve_univariate_inequality
from sympy.utilities import filldedent

def _invert(f_x, y, x, domain=S.Complexes):
"""
Reduce the complex valued equation f(x) = y to a set of equations
{g(x) = h_1(y), g(x) = h_2(y), ..., g(x) = h_n(y) } where g(x) is
a simpler function than f(x).  The return value is a tuple (g(x),
set_h), where g(x) is a function of x and set_h is
the set of function {h_1(y), h_2(y), ..., h_n(y)}.
Here, y is not necessarily a symbol.

The set_h contains the functions along with the information
about their domain in which they are valid, through set
operations. For instance, if y = Abs(x) - n, is inverted
in the real domain, then, the set_h doesn't simply return
{-n, n}, as the nature of n is unknown; rather it will return:
Intersection([0, oo) {n}) U Intersection((-oo, 0], {-n})

By default, the complex domain is used but note that inverting even
seemingly simple functions like exp(x) can give very different
result in the complex domain than are obtained in the real domain.
(In the case of exp(x), the inversion via log is multi-valued
in the complex domain, having infinitely many branches.)

If you are working with real values only (or you are not sure which
function to use) you should probably use set the domain to
S.Reals (or use invert\_real which does that automatically).

Examples
========

>>> from sympy.solvers.solveset import invert_complex, invert_real
>>> from sympy.abc import x, y
>>> from sympy import exp, log

When does exp(x) == y?

>>> invert_complex(exp(x), y, x)
(x, ImageSet(Lambda(_n, I*(2*_n*pi + arg(y)) + log(Abs(y))), Integers()))
>>> invert_real(exp(x), y, x)
(x, Intersection((-oo, oo), {log(y)}))

When does exp(x) == 1?

>>> invert_complex(exp(x), 1, x)
(x, ImageSet(Lambda(_n, 2*_n*I*pi), Integers()))
>>> invert_real(exp(x), 1, x)
(x, {0})

========
invert_real, invert_complex
"""
x = sympify(x)
if not x.is_Symbol:
raise ValueError("x must be a symbol")
f_x = sympify(f_x)
if not f_x.has(x):
raise ValueError("Inverse of constant function doesn't exist")
y = sympify(y)
if y.has(x):
raise ValueError("y should be independent of x ")

if domain.is_subset(S.Reals):
x, s = _invert_real(f_x, FiniteSet(y), x)
else:
x, s = _invert_complex(f_x, FiniteSet(y), x)
return x, s.intersection(domain) if isinstance(s, FiniteSet) else s

invert_complex = _invert

[docs]def invert_real(f_x, y, x, domain=S.Reals): return _invert(f_x, y, x, domain)
def _invert_real(f, g_ys, symbol): """Helper function for _invert.""" if f == symbol: return (f, g_ys) n = Dummy('n', real=True) if hasattr(f, 'inverse') and not isinstance(f, ( TrigonometricFunction, HyperbolicFunction, )): if len(f.args) > 1: raise ValueError("Only functions with one argument are supported.") return _invert_real(f.args[0], imageset(Lambda(n, f.inverse()(n)), g_ys), symbol) if isinstance(f, Abs): pos = Interval(0, S.Infinity) neg = Interval(S.NegativeInfinity, 0) return _invert_real(f.args[0], Union(imageset(Lambda(n, n), g_ys).intersect(pos), imageset(Lambda(n, -n), g_ys).intersect(neg)), symbol) if f.is_Add: # f = g + h g, h = f.as_independent(symbol) if g is not S.Zero: return _invert_real(h, imageset(Lambda(n, n - g), g_ys), symbol) if f.is_Mul: # f = g*h g, h = f.as_independent(symbol) if g is not S.One: return _invert_real(h, imageset(Lambda(n, n/g), g_ys), symbol) if f.is_Pow: base, expo = f.args base_has_sym = base.has(symbol) expo_has_sym = expo.has(symbol) if not expo_has_sym: res = imageset(Lambda(n, real_root(n, expo)), g_ys) if expo.is_rational: numer, denom = expo.as_numer_denom() if numer == S.One or numer == - S.One: return _invert_real(base, res, symbol) else: if numer % 2 == 0: n = Dummy('n') neg_res = imageset(Lambda(n, -n), res) return _invert_real(base, res + neg_res, symbol) else: return _invert_real(base, res, symbol) else: if not base.is_positive: raise ValueError("x**w where w is irrational is not " "defined for negative x") return _invert_real(base, res, symbol) if not base_has_sym: return _invert_real(expo, imageset(Lambda(n, log(n)/log(base)), g_ys), symbol) if isinstance(f, TrigonometricFunction): if isinstance(g_ys, FiniteSet): def inv(trig): if isinstance(f, (sin, csc)): F = asin if isinstance(f, sin) else acsc return (lambda a: n*pi + (-1)**n*F(a),) if isinstance(f, (cos, sec)): F = acos if isinstance(f, cos) else asec return ( lambda a: 2*n*pi + F(a), lambda a: 2*n*pi - F(a),) if isinstance(f, (tan, cot)): return (lambda a: n*pi + f.inverse()(a),) n = Dummy('n', integer=True) invs = S.EmptySet for L in inv(f): invs += Union(*[imageset(Lambda(n, L(g)), S.Integers) for g in g_ys]) return _invert_real(f.args[0], invs, symbol) return (f, g_ys) def _invert_complex(f, g_ys, symbol): """Helper function for _invert.""" if f == symbol: return (f, g_ys) n = Dummy('n') if f.is_Add: # f = g + h g, h = f.as_independent(symbol) if g is not S.Zero: return _invert_complex(h, imageset(Lambda(n, n - g), g_ys), symbol) if f.is_Mul: # f = g*h g, h = f.as_independent(symbol) if g is not S.One: return _invert_complex(h, imageset(Lambda(n, n/g), g_ys), symbol) if hasattr(f, 'inverse') and \ not isinstance(f, TrigonometricFunction) and \ not isinstance(f, exp): if len(f.args) > 1: raise ValueError("Only functions with one argument are supported.") return _invert_complex(f.args[0], imageset(Lambda(n, f.inverse()(n)), g_ys), symbol) if isinstance(f, exp): if isinstance(g_ys, FiniteSet): exp_invs = Union(*[imageset(Lambda(n, I*(2*n*pi + arg(g_y)) + log(Abs(g_y))), S.Integers) for g_y in g_ys if g_y != 0]) return _invert_complex(f.args[0], exp_invs, symbol) return (f, g_ys)
[docs]def domain_check(f, symbol, p): """Returns False if point p is infinite or any subexpression of f is infinite or becomes so after replacing symbol with p. If none of these conditions is met then True will be returned. Examples ======== >>> from sympy import Mul, oo >>> from sympy.abc import x >>> from sympy.solvers.solveset import domain_check >>> g = 1/(1 + (1/(x + 1))**2) >>> domain_check(g, x, -1) False >>> domain_check(x**2, x, 0) True >>> domain_check(1/x, x, oo) False * The function relies on the assumption that the original form of the equation has not been changed by automatic simplification. >>> domain_check(x/x, x, 0) # x/x is automatically simplified to 1 True * To deal with automatic evaluations use evaluate=False: >>> domain_check(Mul(x, 1/x, evaluate=False), x, 0) False """ f, p = sympify(f), sympify(p) if p.is_infinite: return False return _domain_check(f, symbol, p)
def _domain_check(f, symbol, p): # helper for domain check if f.is_Atom and f.is_finite: return True elif f.subs(symbol, p).is_infinite: return False else: return all([_domain_check(g, symbol, p) for g in f.args]) def _is_finite_with_finite_vars(f, domain=S.Complexes): """ Return True if the given expression is finite. For symbols that don't assign a value for complex and/or real, the domain will be used to assign a value; symbols that don't assign a value for finite will be made finite. All other assumptions are left unmodified. """ def assumptions(s): A = s.assumptions0 if A.get('finite', None) is None: A['finite'] = True A.setdefault('complex', True) A.setdefault('real', domain.is_subset(S.Reals)) return A reps = dict([(s, Dummy(**assumptions(s))) for s in f.free_symbols]) return f.xreplace(reps).is_finite def _is_function_class_equation(func_class, f, symbol): """ Tests whether the equation is an equation of the given function class. The given equation belongs to the given function class if it is comprised of functions of the function class which are multiplied by or added to expressions independent of the symbol. In addition, the arguments of all such functions must be linear in the symbol as well. Examples ======== >>> from sympy.solvers.solveset import _is_function_class_equation >>> from sympy import tan, sin, tanh, sinh, exp >>> from sympy.abc import x >>> from sympy.functions.elementary.trigonometric import (TrigonometricFunction, ... HyperbolicFunction) >>> _is_function_class_equation(TrigonometricFunction, exp(x) + tan(x), x) False >>> _is_function_class_equation(TrigonometricFunction, tan(x) + sin(x), x) True >>> _is_function_class_equation(TrigonometricFunction, tan(x**2), x) False >>> _is_function_class_equation(TrigonometricFunction, tan(x + 2), x) True >>> _is_function_class_equation(HyperbolicFunction, tanh(x) + sinh(x), x) True """ if f.is_Mul or f.is_Add: return all(_is_function_class_equation(func_class, arg, symbol) for arg in f.args) if f.is_Pow: if not f.exp.has(symbol): return _is_function_class_equation(func_class, f.base, symbol) else: return False if not f.has(symbol): return True if isinstance(f, func_class): try: g = Poly(f.args[0], symbol) return g.degree() <= 1 except PolynomialError: return False else: return False def _solve_as_rational(f, symbol, domain): """ solve rational functions""" f = together(f, deep=True) g, h = fraction(f) if not h.has(symbol): return _solve_as_poly(g, symbol, domain) else: valid_solns = _solveset(g, symbol, domain) invalid_solns = _solveset(h, symbol, domain) return valid_solns - invalid_solns def _solve_real_trig(f, symbol): """ Helper to solve trigonometric equations """ f = trigsimp(f) f_original = f f = f.rewrite(exp) f = together(f) g, h = fraction(f) y = Dummy('y') g, h = g.expand(), h.expand() g, h = g.subs(exp(I*symbol), y), h.subs(exp(I*symbol), y) if g.has(symbol) or h.has(symbol): return ConditionSet(symbol, Eq(f, 0), S.Reals) solns = solveset_complex(g, y) - solveset_complex(h, y) if isinstance(solns, FiniteSet): return Union(*[invert_complex(exp(I*symbol), s, symbol)[1] for s in solns]) elif solns is S.EmptySet: return S.EmptySet else: return ConditionSet(symbol, Eq(f_original, 0), S.Reals) def _solve_as_poly(f, symbol, domain=S.Complexes): """ Solve the equation using polynomial techniques if it already is a polynomial equation or, with a change of variables, can be made so. """ result = None if f.is_polynomial(symbol): solns = roots(f, symbol, cubics=True, quartics=True, quintics=True, domain='EX') num_roots = sum(solns.values()) if degree(f, symbol) <= num_roots: result = FiniteSet(*solns.keys()) else: poly = Poly(f, symbol) solns = poly.all_roots() if poly.degree() <= len(solns): result = FiniteSet(*solns) else: result = ConditionSet(symbol, Eq(f, 0), domain) else: poly = Poly(f) if poly is None: result = ConditionSet(symbol, Eq(f, 0), domain) gens = [g for g in poly.gens if g.has(symbol)] if len(gens) == 1: poly = Poly(poly, gens[0]) gen = poly.gen deg = poly.degree() poly = Poly(poly.as_expr(), poly.gen, composite=True) poly_solns = FiniteSet(*roots(poly, cubics=True, quartics=True, quintics=True).keys()) if len(poly_solns) < deg: result = ConditionSet(symbol, Eq(f, 0), domain) if gen != symbol: y = Dummy('y') inverter = invert_real if domain.is_subset(S.Reals) else invert_complex lhs, rhs_s = inverter(gen, y, symbol) if lhs == symbol: result = Union(*[rhs_s.subs(y, s) for s in poly_solns]) else: result = ConditionSet(symbol, Eq(f, 0), domain) else: result = ConditionSet(symbol, Eq(f, 0), domain) if result is not None: if isinstance(result, FiniteSet): # this is to simplify solutions like -sqrt(-I) to sqrt(2)/2 # - sqrt(2)*I/2. We are not expanding for solution with free # variables because that makes the solution more complicated. For # example expand_complex(a) returns re(a) + I*im(a) if all([s.free_symbols == set() and not isinstance(s, RootOf) for s in result]): s = Dummy('s') result = imageset(Lambda(s, expand_complex(s)), result) if isinstance(result, FiniteSet): result = result.intersection(domain) return result else: return ConditionSet(symbol, Eq(f, 0), domain) def _has_rational_power(expr, symbol): """ Returns (bool, den) where bool is True if the term has a non-integer rational power and den is the denominator of the expression's exponent. Examples ======== >>> from sympy.solvers.solveset import _has_rational_power >>> from sympy import sqrt >>> from sympy.abc import x >>> _has_rational_power(sqrt(x), x) (True, 2) >>> _has_rational_power(x**2, x) (False, 1) """ a, p, q = Wild('a'), Wild('p'), Wild('q') pattern_match = expr.match(a*p**q) or {} if pattern_match.get(a, S.Zero) is S.Zero: return (False, S.One) elif p not in pattern_match.keys(): return (False, S.One) elif isinstance(pattern_match[q], Rational) \ and pattern_match[p].has(symbol): if not pattern_match[q].q == S.One: return (True, pattern_match[q].q) if not isinstance(pattern_match[a], Pow) \ or isinstance(pattern_match[a], Mul): return (False, S.One) else: return _has_rational_power(pattern_match[a], symbol) def _solve_radical(f, symbol, solveset_solver): """ Helper function to solve equations with radicals """ eq, cov = unrad(f) if not cov: result = solveset_solver(eq, symbol) - \ Union(*[solveset_solver(g, symbol) for g in denoms(f, [symbol])]) else: y, yeq = cov if not solveset_solver(y - I, y): yreal = Dummy('yreal', real=True) yeq = yeq.xreplace({y: yreal}) eq = eq.xreplace({y: yreal}) y = yreal g_y_s = solveset_solver(yeq, symbol) f_y_sols = solveset_solver(eq, y) result = Union(*[imageset(Lambda(y, g_y), f_y_sols) for g_y in g_y_s]) return FiniteSet(*[s for s in result if checksol(f, symbol, s) is True]) def _solve_abs(f, symbol, domain): """ Helper function to solve equation involving absolute value function """ if not domain.is_subset(S.Reals): raise ValueError(filldedent(''' Absolute values cannot be inverted in the complex domain.''')) p, q, r = Wild('p'), Wild('q'), Wild('r') pattern_match = f.match(p*Abs(q) + r) or {} if not pattern_match.get(p, S.Zero).is_zero: f_p, f_q, f_r = pattern_match[p], pattern_match[q], pattern_match[r] q_pos_cond = solve_univariate_inequality(f_q >= 0, symbol, relational=False) q_neg_cond = solve_univariate_inequality(f_q < 0, symbol, relational=False) sols_q_pos = solveset_real(f_p*f_q + f_r, symbol).intersect(q_pos_cond) sols_q_neg = solveset_real(f_p*(-f_q) + f_r, symbol).intersect(q_neg_cond) return Union(sols_q_pos, sols_q_neg) else: return ConditionSet(symbol, Eq(f, 0), domain) def _solveset(f, symbol, domain, _check=False): """Helper for solveset to return a result from an expression that has already been sympify'ed and is known to contain the given symbol.""" # _check controls whether the answer is checked or not from sympy.simplify.simplify import signsimp orig_f = f f = together(f) if f.is_Mul: _, f = f.as_independent(symbol, as_Add=False) if f.is_Add: a, h = f.as_independent(symbol) m, h = h.as_independent(symbol, as_Add=False) f = a/m + h # XXX condition m != 0 should be added to soln f = piecewise_fold(f) # assign the solvers to use solver = lambda f, x, domain=domain: _solveset(f, x, domain) if domain.is_subset(S.Reals): inverter_func = invert_real else: inverter_func = invert_complex inverter = lambda f, rhs, symbol: inverter_func(f, rhs, symbol, domain) result = EmptySet() if f.expand().is_zero: return domain elif not f.has(symbol): return EmptySet() elif f.is_Mul and all(_is_finite_with_finite_vars(m, domain) for m in f.args): # if f(x) and g(x) are both finite we can say that the solution of # f(x)*g(x) == 0 is same as Union(f(x) == 0, g(x) == 0) is not true in # general. g(x) can grow to infinitely large for the values where # f(x) == 0. To be sure that we are not silently allowing any # wrong solutions we are using this technique only if both f and g are # finite for a finite input. result = Union(*[solver(m, symbol) for m in f.args]) elif _is_function_class_equation(TrigonometricFunction, f, symbol) or \ _is_function_class_equation(HyperbolicFunction, f, symbol): result = _solve_real_trig(f, symbol) elif f.is_Piecewise: dom = domain result = EmptySet() expr_set_pairs = f.as_expr_set_pairs() for (expr, in_set) in expr_set_pairs: if in_set.is_Relational: in_set = in_set.as_set() if in_set.is_Interval: dom -= in_set solns = solver(expr, symbol, in_set) result += solns else: lhs, rhs_s = inverter(f, 0, symbol) if lhs == symbol: # do some very minimal simplification since # repeated inversion may have left the result # in a state that other solvers (e.g. poly) # would have simplified; this is done here # rather than in the inverter since here it # is only done once whereas there it would # be repeated for each step of the inversion if isinstance(rhs_s, FiniteSet): rhs_s = FiniteSet(*[Mul(* signsimp(i).as_content_primitive()) for i in rhs_s]) result = rhs_s elif isinstance(rhs_s, FiniteSet): for equation in [lhs - rhs for rhs in rhs_s]: if equation == f: if any(_has_rational_power(g, symbol)[0] for g in equation.args) or _has_rational_power( equation, symbol)[0]: result += _solve_radical(equation, symbol, solver) elif equation.has(Abs): result += _solve_abs(f, symbol, domain) else: result += _solve_as_rational(equation, symbol, domain) else: result += solver(equation, symbol) else: result = ConditionSet(symbol, Eq(f, 0), domain) if _check: if isinstance(result, ConditionSet): # it wasn't solved or has enumerated all conditions # -- leave it alone return result # whittle away all but the symbol-containing core # to use this for testing fx = orig_f.as_independent(symbol, as_Add=True)[1] fx = fx.as_independent(symbol, as_Add=False)[1] if isinstance(result, FiniteSet): # check the result for invalid solutions result = FiniteSet(*[s for s in result if isinstance(s, RootOf) or domain_check(fx, symbol, s)]) return result
[docs]def solveset(f, symbol=None, domain=S.Complexes): """Solves a given inequality or equation with set as output Parameters ========== f : Expr or a relational. The target equation or inequality symbol : Symbol The variable for which the equation is solved domain : Set The domain over which the equation is solved Returns ======= Set A set of values for symbol for which f is True or is equal to zero. An EmptySet is returned if f is False or nonzero. A ConditionSet is returned as unsolved object if algorithms to evaluatee complete solution are not yet implemented. solveset claims to be complete in the solution set that it returns. Raises ====== NotImplementedError The algorithms to solve inequalities in complex domain are not yet implemented. ValueError The input is not valid. RuntimeError It is a bug, please report to the github issue tracker. Notes ===== Python interprets 0 and 1 as False and True, respectively, but in this function they refer to solutions of an expression. So 0 and 1 return the Domain and EmptySet, respectively, while True and False return the opposite (as they are assumed to be solutions of relational expressions). See Also ======== solveset_real: solver for real domain solveset_complex: solver for complex domain Examples ======== >>> from sympy import exp, sin, Symbol, pprint, S >>> from sympy.solvers.solveset import solveset, solveset_real * The default domain is complex. Not specifying a domain will lead to the solving of the equation in the complex domain (and this is not affected by the assumptions on the symbol): >>> x = Symbol('x') >>> pprint(solveset(exp(x) - 1, x), use_unicode=False) {2*n*I*pi | n in Integers()} >>> x = Symbol('x', real=True) >>> pprint(solveset(exp(x) - 1, x), use_unicode=False) {2*n*I*pi | n in Integers()} * If you want to use solveset to solve the equation in the real domain, provide a real domain. (Using solveset\_real does this automatically.) >>> R = S.Reals >>> x = Symbol('x') >>> solveset(exp(x) - 1, x, R) {0} >>> solveset_real(exp(x) - 1, x) {0} The solution is mostly unaffected by assumptions on the symbol, but there may be some slight difference: >>> pprint(solveset(sin(x)/x,x), use_unicode=False) ({2*n*pi | n in Integers()} \ {0}) U ({2*n*pi + pi | n in Integers()} \ {0}) >>> p = Symbol('p', positive=True) >>> pprint(solveset(sin(p)/p, p), use_unicode=False) {2*n*pi | n in Integers()} U {2*n*pi + pi | n in Integers()} * Inequalities can be solved over the real domain only. Use of a complex domain leads to a NotImplementedError. >>> solveset(exp(x) > 1, x, R) (0, oo) """ f = sympify(f) if f is S.true: return domain if f is S.false: return S.EmptySet if not isinstance(f, (Expr, Number)): raise ValueError("%s is not a valid SymPy expression" % (f)) free_symbols = f.free_symbols if not free_symbols: b = Eq(f, 0) if b is S.true: return domain elif b is S.false: return S.EmptySet else: raise NotImplementedError(filldedent(''' relationship between value and 0 is unknown: %s''' % b)) if symbol is None: if len(free_symbols) == 1: symbol = free_symbols.pop() else: raise ValueError(filldedent(''' The independent variable must be specified for a multivariate equation.''')) elif not getattr(symbol, 'is_Symbol', False): raise ValueError('A Symbol must be given, not type %s: %s' % (type(symbol), symbol)) if isinstance(f, Eq): from sympy.core import Add f = Add(f.lhs, - f.rhs, evaluate=False) elif f.is_Relational: if not domain.is_subset(S.Reals): raise NotImplementedError(filldedent(''' Inequalities in the complex domain are not supported. Try the real domain by setting domain=S.Reals''')) try: result = solve_univariate_inequality( f, symbol, relational=False) - _invalid_solutions( f, symbol, domain) except NotImplementedError: result = ConditionSet(symbol, f, domain) return result return _solveset(f, symbol, domain, _check=True)
def _invalid_solutions(f, symbol, domain): bad = S.EmptySet for d in denoms(f): bad += _solveset(d, symbol, domain, _check=False) return bad
[docs]def solveset_real(f, symbol): return solveset(f, symbol, S.Reals)
[docs]def solveset_complex(f, symbol): return solveset(f, symbol, S.Complexes) ############################################################################### ################################ LINSOLVE ##################################### ###############################################################################
[docs]def linear_eq_to_matrix(equations, *symbols): r""" Converts a given System of Equations into Matrix form. Here equations must be a linear system of equations in symbols. The order of symbols in input symbols will determine the order of coefficients in the returned Matrix. The Matrix form corresponds to the augmented matrix form. For example: .. math:: 4x + 2y + 3z = 1 .. math:: 3x + y + z = -6 .. math:: 2x + 4y + 9z = 2 This system would return A & b as given below: :: [ 4 2 3 ] [ 1 ] A = [ 3 1 1 ] b = [-6 ] [ 2 4 9 ] [ 2 ] Examples ======== >>> from sympy import linear_eq_to_matrix, symbols >>> x, y, z = symbols('x, y, z') >>> eqns = [x + 2*y + 3*z - 1, 3*x + y + z + 6, 2*x + 4*y + 9*z - 2] >>> A, b = linear_eq_to_matrix(eqns, [x, y, z]) >>> A Matrix([ [1, 2, 3], [3, 1, 1], [2, 4, 9]]) >>> b Matrix([ [ 1], [-6], [ 2]]) >>> eqns = [x + z - 1, y + z, x - y] >>> A, b = linear_eq_to_matrix(eqns, [x, y, z]) >>> A Matrix([ [1, 0, 1], [0, 1, 1], [1, -1, 0]]) >>> b Matrix([ [1], [0], [0]]) * Symbolic coefficients are also supported >>> a, b, c, d, e, f = symbols('a, b, c, d, e, f') >>> eqns = [a*x + b*y - c, d*x + e*y - f] >>> A, B = linear_eq_to_matrix(eqns, x, y) >>> A Matrix([ [a, b], [d, e]]) >>> B Matrix([ [c], [f]]) """ if not symbols: raise ValueError('Symbols must be given, for which coefficients \ are to be found.') if hasattr(symbols[0], '__iter__'): symbols = symbols[0] M = Matrix([symbols]) # initialise Matrix with symbols + 1 columns M = M.col_insert(len(symbols), Matrix([1])) row_no = 1 for equation in equations: f = sympify(equation) if isinstance(f, Equality): f = f.lhs - f.rhs # Extract coeff of symbols coeff_list = [] for symbol in symbols: coeff_list.append(f.coeff(symbol)) # append constant term (term free from symbols) coeff_list.append(-f.as_coeff_add(*symbols)[0]) # insert equations coeff's into rows M = M.row_insert(row_no, Matrix([coeff_list])) row_no += 1 # delete the initialised (Ist) trivial row M.row_del(0) A, b = M[:, :-1], M[:, -1:] return A, b
[docs]def linsolve(system, *symbols): r""" Solve system of N linear equations with M variables, which means both under - and overdetermined systems are supported. The possible number of solutions is zero, one or infinite. Zero solutions throws a ValueError, where as infinite solutions are represented parametrically in terms of given symbols. For unique solution a FiniteSet of ordered tuple is returned. All Standard input formats are supported: For the given set of Equations, the respective input types are given below: .. math:: 3x + 2y - z = 1 .. math:: 2x - 2y + 4z = -2 .. math:: 2x - y + 2z = 0 * Augmented Matrix Form, system given below: :: [3 2 -1 1] system = [2 -2 4 -2] [2 -1 2 0] * List Of Equations Form system = [3x + 2y - z - 1, 2x - 2y + 4z + 2, 2x - y + 2z] * Input A & b Matrix Form (from Ax = b) are given as below: :: [3 2 -1 ] [ 1 ] A = [2 -2 4 ] b = [ -2 ] [2 -1 2 ] [ 0 ] system = (A, b) Symbols to solve for should be given as input in all the cases either in an iterable or as comma separated arguments. This is done to maintain consistency in returning solutions in the form of variable input by the user. The algorithm used here is Gauss-Jordan elimination, which results, after elimination, in an row echelon form matrix. Returns ======= A FiniteSet of ordered tuple of values of symbols for which the system has solution. Please note that general FiniteSet is unordered, the solution returned here is not simply a FiniteSet of solutions, rather it is a FiniteSet of ordered tuple, i.e. the first & only argument to FiniteSet is a tuple of solutions, which is ordered, & hence the returned solution is ordered. Also note that solution could also have been returned as an ordered tuple, FiniteSet is just a wrapper {} around the tuple. It has no other significance except for the fact it is just used to maintain a consistent output format throughout the solveset. Returns EmptySet(), if the linear system is inconsistent. Raises ====== ValueError The input is not valid. The symbols are not given. Examples ======== >>> from sympy import Matrix, S, linsolve, symbols >>> x, y, z = symbols("x, y, z") >>> A = Matrix([[1, 2, 3], [4, 5, 6], [7, 8, 10]]) >>> b = Matrix([3, 6, 9]) >>> A Matrix([ [1, 2, 3], [4, 5, 6], [7, 8, 10]]) >>> b Matrix([ [3], [6], [9]]) >>> linsolve((A, b), [x, y, z]) {(-1, 2, 0)} * Parametric Solution: In case the system is under determined, the function will return parametric solution in terms of the given symbols. Free symbols in the system are returned as it is. For e.g. in the system below, z is returned as the solution for variable z, which means z is a free symbol, i.e. it can take arbitrary values. >>> A = Matrix([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) >>> b = Matrix([3, 6, 9]) >>> linsolve((A, b), [x, y, z]) {(z - 1, -2*z + 2, z)} * List of Equations as input >>> Eqns = [3*x + 2*y - z - 1, 2*x - 2*y + 4*z + 2, - x + S(1)/2*y - z] >>> linsolve(Eqns, x, y, z) {(1, -2, -2)} * Augmented Matrix as input >>> aug = Matrix([[2, 1, 3, 1], [2, 6, 8, 3], [6, 8, 18, 5]]) >>> aug Matrix([ [2, 1, 3, 1], [2, 6, 8, 3], [6, 8, 18, 5]]) >>> linsolve(aug, x, y, z) {(3/10, 2/5, 0)} * Solve for symbolic coefficients >>> a, b, c, d, e, f = symbols('a, b, c, d, e, f') >>> eqns = [a*x + b*y - c, d*x + e*y - f] >>> linsolve(eqns, x, y) {((-b*f + c*e)/(a*e - b*d), (a*f - c*d)/(a*e - b*d))} * A degenerate system returns solution as set of given symbols. >>> system = Matrix(([0,0,0], [0,0,0], [0,0,0])) >>> linsolve(system, x, y) {(x, y)} * For an empty system linsolve returns empty set >>> linsolve([ ], x) EmptySet() """ if not system: return S.EmptySet if not symbols: raise ValueError('Symbols must be given, for which solution of the ' 'system is to be found.') if hasattr(symbols[0], '__iter__'): symbols = symbols[0] try: sym = symbols[0].is_Symbol except AttributeError: sym = False if not sym: raise ValueError('Symbols or iterable of symbols must be given as ' 'second argument, not type %s: %s' % (type(symbols[0]), symbols[0])) # 1). Augmented Matrix input Form if isinstance(system, Matrix): A, b = system[:, :-1], system[:, -1:] elif hasattr(system, '__iter__'): # 2). A & b as input Form if len(system) == 2 and system[0].is_Matrix: A, b = system[0], system[1] # 3). List of equations Form if not system[0].is_Matrix: A, b = linear_eq_to_matrix(system, symbols) else: raise ValueError("Invalid arguments") # Solve using Gauss-Jordan elimination try: sol, params, free_syms = A.gauss_jordan_solve(b, freevar=True) except ValueError: # No solution return EmptySet() # Replace free parameters with free symbols solution = [] if params: for s in sol: for k, v in enumerate(params): s = s.xreplace({v: symbols[free_syms[k]]}) solution.append(simplify(s)) else: for s in sol: solution.append(simplify(s)) # Return solutions solution = FiniteSet(tuple(solution)) return solution