chemical_equation_balancer/equation_solver.py

from fractions import Fraction

import numpy as np
import scipy as sp


def solve_equation(eq):
    """
    配平化学方程式，返回配平后的化学方程式

    :param eq: 化学方程式，
    格式为
    {
        'left': [ {
                    'atoms': [ {'元素名称': 元素个数}, {'元素名称': 元素个数}, ... ],
                    'coefficient': 系数,
                    'pretty_name': 化学式的字符串表示
                  }, ... ],
        'right': [ ... ]
    }
    :return: 配平后的化学方程式，与输入格式相同
    若无法配平，则返回 None
    """
    # 统计所有元素的种类
    elements = set()
    for each in eq['left']:
        for atom in each['atoms']:
            elements.add(list(atom.keys())[0])
    for each in eq['right']:
        for atom in each['atoms']:
            elements.add(list(atom.keys())[0])
    elements = list(elements)
    # 构造系数矩阵
    matrix = []
    constant = []
    for atom in elements:
        # 遍历左边，左侧系数为正
        row = []
        for each in eq['left']:
            for atom_ in each['atoms']:
                if atom in atom_:
                    row.append(atom_[atom])
                    break
            else:
                row.append(0)
        # 遍历右边，右侧系数为负
        for each in eq['right']:
            for atom_ in each['atoms']:
                if atom in atom_:
                    row.append(-atom_[atom])
                    break
            else:
                row.append(0)
        # 取出row中的最后一个元素，反转后加入常数项
        constant.append(-row.pop())
        matrix.append(row)
    matrix = np.mat(matrix, int)
    # 求解线性方程组
    try:
        result = sp.optimize.lsq_linear(matrix, constant, bounds=(0, None)).x.tolist()
    except ValueError:
        raise ValueError('无法配平')

    # 将结果写入化学方程式，最后一个生成物的系数需要计算得到
    last_substance = eq['right'][-1]
    last_atom = list(last_substance['atoms'][0].keys())[0]
    # 计算除最后一种生成物外的所有生成物包含last_atom的系数之和
    sum_ = 0
    index = 0
    for each in eq['left']:
        for atom in each['atoms']:
            if last_atom in atom:
                # 该生成物包含last_atom，则获得last_atom的总个数，等于系数*原子个数
                sum_ += result[index] * atom[last_atom]
                break
        index += 1
    for each in eq['right'][:-1]:
        for atom in each['atoms']:
            if last_atom in atom:
                sum_ -= result[index] * atom[last_atom]
                break
        index += 1
    result.append(sum_ / last_substance['atoms'][0][last_atom])
    result = expand_to_int(*result)
    for i, each in enumerate(eq['left']):
        each['coefficient'] = result[i]
    for i, each in enumerate(eq['right']):
        each['coefficient'] = result[i + len(eq['left'])]
    return eq


def expand_to_int(*args):
    """
    将一系列小数同时扩大，全部转换为最接近的整数

    :param args: 一系列小数
    :return: 一系列整数
    """
    # 将所有小数转换为分数
    fractions = []
    for each in args:
        fractions.append(Fraction(each).limit_denominator())
    # 计算所有分数的最小公倍数
    lcm = 1
    for each in fractions:
        lcm = lcm * each.denominator // np.gcd(lcm, each.denominator)
    # 将所有分数扩大为最小公倍数
    result = []
    for each in fractions:
        result.append(each.numerator * lcm // each.denominator)
    return result