利用solve解方程报错

Question

import math
import numpy as np
from sympy import *
k=Symbol("k")
def fv_ans(pmt,i,n):
    fv_up=pmt/i
    fv_down=(1+i)**n-1
    fv=fv_up*fv_down
    return fv
def pv_ans(pmt,i,n):
    pv_up=pmt/i
    pv_down=1-(1+i)**(-n)
    pv=pv_up*pv_down
fv_future = fv_ans(300000-k,0.03,25)
fv_present=fv_ans(25000-k,0.03,5)*(1.03**25)
pv_ans=pv_ans(k,0.03,20)
pmt_1=300000-k
i_1=0.03
n_1=25
pmt_2=25000-k
i_2=0.03
n_2=5
pmt_3=k
i_3=0.03
n_3=20
print(solve([((pmt_1/i_1)*(1+i_1)**n_1-1+((pmt_2/i_2)*(1+i_2)**n_2-1)*(1.03**25))-pmt_3/i_3*(1-(1+i_3)**(-n_3))],[k]))
print(solve([fv_future+fv_present-pv_ans],[k]))

代码在倒数第二行可以输出结果而倒数第一行不行，但我想让它们执行的运算是一样的

Answer 1

你这个函数没有返回

def pv_ans(pmt, i, n):
    pv_up = pmt / i
    pv_down = 1 - (1 + i) ** (-n)
    pv = pv_up * pv_down

按下面修改即可正确

def pv_ans(pmt, i, n):
    pv_up = pmt / i
    pv_down = 1 - (1 + i) ** (-n)
    pv = pv_up * pv_down
    return  pv

有帮助请采纳,有问题继续交流,你的采纳是对我回答的最大的肯定和动力