巢状清单无法正常运作 [英] Nested list doesn't work properly

问题描述

import re
def get_number(element):
    re_number = re.match("(\d+\.?\d*)", element)

    if re_number:
        return float(re_number.group(1))
    else:
        return 1.0

def getvalues(equation):
    elements = re.findall("([a-z0-9.]+)", equation)
    return [get_number(element) for element in elements]


eqn = []
eqn_no = int(raw_input("Enter the number of equations: "))

for i in range(eqn_no):
    eqn.append(getvalues(str(raw_input("Enter Equation %d: " % (i+1)))))
print "Main Matrix: "
for i in range((eqn_no)):
    for j in range((eqn_no+1)):
        print "\t%f" %(eqn[i][j]),
    print
print
equation=[]
equation=eqn
for k in range((eqn_no-1)):
    for i in range((k+1),eqn_no):
        for j in range((eqn_no+1)):
            if(eqn[i][j]!=0):
                eqn[i][j]=eqn[i][j]-(eqn[k][j]*(equation[i][k]/eqn[k][k]))



    print "Matrix After %d step: " %(k+1)
    for i in range(eqn_no):
            for j in range((eqn_no+1)):
                print "\t%f"%(eqn[i][j]),
                equation[i][j]=eqn[i][j];

            print
    print

输入:

25x+5y+z=106.8
64x+8y+z=177.2
144x+12y+z=279.2

输出为:

Main Matrix: 
    25.000000   5.000000    1.000000    106.800000
    64.000000   8.000000    1.000000    177.200000
    144.000000  12.000000   1.000000    279.200000

Matrix After 1 step: 
    25.000000   5.000000    1.000000    106.800000
    0.000000    8.000000    1.000000    177.200000
    0.000000    12.000000   1.000000    279.200000

Matrix After 2 step: 
    25.000000   5.000000    1.000000    106.800000
    0.000000    8.000000    1.000000    177.200000
    0.000000    0.000000    1.000000    279.200000

但是应该像

Main Matrix: 
    25.000000   5.000000    1.000000    106.800000
    64.000000   8.000000    1.000000    177.200000
    144.000000  12.000000   1.000000    279.200000

Matrix After 1 step: 
    25.000000   5.000000    1.000000    106.800000
    0.000000    -4.80000    -1.56000    -96.208000
    0.000000    -16.8000    -4.76000    -335.968000

Matrix After 2 step: 
    25.000000   5.000000    1.000000    106.800000
    0.000000    -4.80000    -1.56000    -96.208000
    0.000000    0.000000    0.699999    0.759981

首先，这是一个部分代码，用于使用朴素Guass消除方法求解n个方程式的根.有谁知道为什么发生这种情况?为什么零部分在变化而其他部分没有变化?我已经在c ++中完成了这段代码，并且在这里可以完美地工作，但是在这里我面临很多问题.也许我是python的新手.我正在使用python 2.7 .....

First of all this is a partial code for solving root of n number of equations using Naive Guass elemination method. Does anyone have any idea why the hell on earth is this happening? Why the zero parts are changing and others aren't? I have done this code in c++ and it works there perfectly but here I'm facing many problem. Maybe I'm newbie to python. I'm using python 2.7.....

推荐答案

我认为问题是作业equation = eqn.由于eqn是一个列表，因此它是可变的，因此作为引用传递，当您分配可变变量时，该变量实际上包含指向该对象的指针.这意味着equation和eqn是相同的列表.

I think the problem is the assignment equation = eqn. Since eqn is a list, it is a mutable and thus passed as a reference, when you assign a mutable, the variable actually contains a pointer to that object. This means that equation and eqn are the same list.

您应该

from copy import deepcopy
equation = deepcopy(eqn)

您需要deepcopy而不是copy，因为您有一个列表列表，而且内部列表也需要复制.

You need deepcopy instead of copy because you have a list of lists, also the inner list needs to be copied.

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