What is problem?..

[yark]

# -*- coding: cp949 -*-

#작은 전류 요소에 의한 자기장

#저자: 

#날짜: 2016-12-01

from visual import *

scene.height = scene.width = 800

L = 5.e3

scene.range = L

#상수

m_const = 1.e-7 #자기 상수

#작은 전류 요소

source_current = 1.   #전류(암페어)

source_axis = vector(0, 0.01*L, 0) #dl 벡터

source_pos = vector(0,-10*L,0) #위치

curve(pos=[(0, -10*L, 0),(0, 10*L, 0)], color=color.green)#dl 방향 연장선

#관찰 위치

obs_radius = 0.4*L #관찰 위치 반지름

d_theta = pi/3.

length = 2*L #자기장을 그릴 전체 거리

obs_y = -10*L #최초 관찰 위치 y 좌표

dy = L/10 #관찰 위치 증가분

obs = [vector(0,-10*L,0)] #관찰 위치 리스트

obs1 = vector(0,-10*L,0)

while obs1.y < 10*L:

    rate(100)

    obs1.y += L/10

    obs.append(obs1)

print obs

#자기장  

scale_factor_m = 2.e-10 #자기장 화살표 스케일

m_field_origin = vector(0,0,0)

i = 0

for hello in obs:

    r = hello - vector(0.05*obs_radius,0,0) #전류에서 보는 관찰 점의 상대 위치

    r_hat = r/mag(r) #상대위치의 단위 벡터

    if i==len(obs)-1:

        i = i-1

    m_field = m_const*source_current*cross(obs[i+1]-obs[i],r_hat)/mag(r)**2#자기장

    i = i+1

    source_pos.y += dy

    m_field_origin += m_field

print "유한한 길이의 도선에 의한 자기장= ", mag(m_field_origin)

m_inf_field = 4.*pi*10**-7*source_current/(2.*pi*obs_radius)

print "무한한 길이의 도선에 의한 자기장= ",m_inf_field

print "Done!!!"

I made this program. I want to increase obs1.y as much as 500 in while formal, but if I print list 'obs' , list 'obs'  is [vector(0, -50000, 0), vector(0, 50000, 0), vector(0, 50000, 0), vector(0, 50000, 0), vector(0, 50000, 0), vector(0, 50000, 0), vector(0, 50000, 0), ...., vector(0,50000,0)]. This is not result that I want. What is problem??

[Bruce Sherwood]

This is a subtle Python issue associated with "mutable" objects such as lists and vectors. When you change the y component of obs1, you do not create a new copy of obs1, you simply modify the vector object obs1. In your while loop you construct a list that looks like this:

obs is [vector(0,-10*L,0), obs1, obs1, obs1, obs1, .....]

where obs1 has the last value assigned to it, namely vector(0, 50000, 0).

One way to get what you want is with this: obs.append( vector(0,obs1.y,0) )

Minor point: You do not need a rate statement in that while loop. A rate statement is needed only if you want changes to visual objects to be seen during the loop.