matplotlib plot 显示不必要的对角线

Question

So I'm trying to plot the approximation of an equation using Euler's method, and it works, the only problem is that the plot shows a diagonal line from the first point to the last, when I use a symbol to plot '<' ,这条线不见了，但我需要一条连续的线。

from decimal import *
#The Decimals are so that x is precise
from matplotlib import pyplot as pyplot

#Creates a range but with floats
def rangoFloat(m,maximo,cre): 
    minimo=Decimal(m)
    n=str(cre)
    while minimo <= maximo:
        yield float(minimo)
        minimo += Decimal(n)

#Substracs xn and delta
def ant(xn,delta): 
    return (float(Decimal(xn)-Decimal(delta)))


#Main function
def Teuler(x0,y0,A,B,cre=0.1,limite=20,delta=5,arr=([],[])): 
    y1=float(y0)
    arr[0].append(x0)
    arr[1].append(y0)
    for i in rangoFloat(ant(x0,-cre),limite,cre):

        arr[0].append(i)
        y1=float(Decimal(y1) * (Decimal(1) + Decimal(cre) * Decimal(A) - Decimal(cre) * Decimal(B)))
        arr[1].append(y1)
        
    return arr

当我运行下一个图时，会出现对角线

t1=Teuler(0, 1, 0.1, 0.16524,0.1,240)
t01 = Teuler(0, 1, 0.1, 0.16524,0.1,240)
t001=Teuler(0, 1, 0.1, 0.16524,0.01,240)
t0005= Teuler(0, 1, 0.1, 0.16524,0.0005,240)
pyplot.grid()
pyplot.plot(t1[0],t1[1])
pyplot.plot(t01[0], t01[1])
pyplot.plot(t001[0], t001[1])
pyplot.plot(t0005[0], t0005[1])
pyplot.show()

我正在使用 python 3.7

Answer 1

出现问题是因为您使用可变类型作为默认参数（ ([],[]) ）。 每个新的 function Teuler调用都会重用相同的 arrays。 您可以通过在Teuler的开头添加print语句来查看它：

print('arr length: ', len(arr[0]), len(arr[0]))

调用后：

t1=Teuler(0, 1, 0.1, 0.16524,0.1,240)
t01 = Teuler(0, 1, 0.1, 0.16524,0.1,240)
t001=Teuler(0, 1, 0.1, 0.16524,0.01,240)
t0005= Teuler(0, 1, 0.1, 0.16524,0.0005,240)
arr length:  0 0
arr length:  2400 2400
arr length:  4800 4800
arr length:  28800 28800

所以，你的t... arrays 从头开始多次，这就是对角线的证据。 您需要做的是是否将可变类显式传递为 arguments 或更改代码以防止 arrays 重用，例如：

#Main function
def Teuler(x0,y0,A,B,cre=0.1,limite=20,delta=5,arr=None):
    if arr is None:
        arr = ([],[])

如需进一步阅读，可以推荐Python 反模式