Python二次公式计算不准确答案

【问题标题】：Python Quadratic Formula Not Calculating AccuratelyPython二次公式计算不准确
【发布时间】：2019-08-28 10:24:15
【问题描述】：

这是我运行程序的主文件：

import math
import Disc

def main():

    coeffA = int(input('Enter the coefficient A: '))
    coeffB = int(input('Enter the coefficient B: '))
    coeffC = int(input('Enter the coefficient C: '))

    disc = Disc.discriminant(coeffA, coeffB, coeffC)

    while coeffA != 0:


        if disc > 0:

            solutionOne = (-coeffB + math.sqrt(disc)) / (2 * coeffA)
            solutionTwo = (-coeffB - math.sqrt(disc)) / (2 * coeffA)

            print('Solutions are: ' + str(solutionOne) + ' and ' + str(solutionTwo))

            coeffA = int(input('Enter the coefficient A: '))
            coeffB = int(input('Enter the coefficient B: '))
            coeffC = int(input('Enter the coefficient C: '))

        elif disc == 0:

            solutionOne = -coeffB / (2 * coeffA)

            print('Solution is: ' + str(solutionOne))

            coeffA = int(input('Enter the coefficient A: '))
            coeffB = int(input('Enter the coefficient B: '))
            coeffC = int(input('Enter the coefficient C: '))

        elif disc < 0:

            print('Equation has two complex roots.')

            coeffA = int(input('Enter the coefficient A: '))
            coeffB = int(input('Enter the coefficient B: '))
            coeffC = int(input('Enter the coefficient C: '))

    else:
        print('Program ended.')


# End of the main function

main()

这是 Disc.py 文件，其中计算判别值以用于 main() 函数：

def discriminant(coeffA, coeffB, coeffC):

    value = (coeffB ** 2) - (4 * coeffA * coeffC)

    return value

这是运行程序时的输出：

Enter the coefficient A: 1
Enter the coefficient B: 2
Enter the coefficient C: -8
Solutions are: 2.0 and -4.0
Enter the coefficient A: 1
Enter the coefficient B: -12
Enter the coefficient C: 36
Solutions are: 9.0 and 3.0
Enter the coefficient A: 2
Enter the coefficient B: 9
Enter the coefficient C: -5
Solutions are: -0.75 and -3.75
Enter the coefficient A: 4
Enter the coefficient B: 6
Enter the coefficient C: 20
Solutions are: 0.0 and -1.5
Enter the coefficient A: 0
Enter the coefficient B: 0
Enter the coefficient C: 0
Program ended.

我期望上面的输入有以下根：

Run1: 2, -4

Run2: 6

Run3: .5, -5

Run4: 'Equation has two complex roots.'

当我运行程序时，程序运行的最后 3 次输出是错误的，并且似乎将判别式设置为大于 0 的值，而我希望它根据计算出的判别式改变输出。提前致谢！

【问题讨论】：

你输入的数字是整数还是小数
'...在我尝试过的所有输入中。 ' - 请提供一些示例输入以及您获得的输出与预期的输出。
你的数字有多差？您尝试了哪些数字？
所有输入都是整数。我用过：a=1,b=2,c=-8, and a=1,b=-12, and c=36
请添加您的期望值，您获得的值并对其进行硬编码以使其成为minimal reproducible example

标签： python python-3.x python-module

【解决方案1】：

您似乎缺少一对括号。这应该可以修复错误：

if disc > 0:

            solutionOne = (-coeffB + math.sqrt(disc)) / (2 * coeffA)
            solutionTwo = (-coeffB - math.sqrt(disc)) / (2 * coeffA)

            print('Solutions are: ' + str(solutionOne) + ' and ' + str(solutionTwo))

            coeffA = int(input('Enter the coefficient A: '))
            coeffB = int(input('Enter the coefficient B: '))
            coeffC = int(input('Enter the coefficient C: '))

【讨论】：

【解决方案2】：

找到了解决方案。我的判别函数在 while 语句之外，所以当用户输入 3 个变量时，它会在每个循环中计算第一个判别式，这就是为什么每次运行输出都会产生 2 个答案的原因。通过将判别函数的位置更改为 while 语句内部，它现在为 while 语句的每个循环重新计算判别式。这是解决这个问题的正确代码：

import math
import Disc

def main():



    coeffA = int(input('Enter the coefficient A: '))

    while coeffA != 0:

        coeffB = int(input('Enter the coefficient B: '))
        coeffC = int(input('Enter the coefficient C: '))

        disc = Disc.discriminant(coeffA, coeffB, coeffC)

        if disc > 0:

            solutionOne = (-coeffB + math.sqrt(disc)) / (2 * coeffA)
            solutionTwo = (-coeffB - math.sqrt(disc)) / (2 * coeffA)

            print('Solutions are: ' + str(solutionOne) + ' and ' + str(solutionTwo))

            coeffA = int(input('Enter the coefficient A: '))

        elif disc == 0:

            solutionOne = -coeffB / (2 * coeffA)

            print('Solution is: ' + str(solutionOne))

            coeffA = int(input('Enter the coefficient A: '))

        elif disc < 0:

            print('Equation has two complex roots.')

            coeffA = int(input('Enter the coefficient A: '))

    print('Program ended.')


    # End of the main function

产生的正确输出代码如下：

Enter the coefficient A: 1
Enter the coefficient B: 2
Enter the coefficient C: -8
Solutions are: 2.0 and -4.0
Enter the coefficient A: 1
Enter the coefficient B: -12
Enter the coefficient C: 36
Solution is: 6.0
Enter the coefficient A: 2
Enter the coefficient B: 9
Enter the coefficient C: -5
Solutions are: 0.5 and -5.0
Enter the coefficient A: 4
Enter the coefficient B: 6
Enter the coefficient C: 20
Equation has two complex roots.
Enter the coefficient A: 0
Program ended.

感谢 Stack Overflow 社区的所有帮助和建议！

【讨论】：