我无法弄清楚为什么我的Reverse Cuthill-McKee算法的实现正在返回 在错误的地方。 基本上,它会产生正确的结果,但是当我运行代码时,它会返回一个不同的值。
这是一个带图表的完整代码,有人可以解释一下这种行为吗?
import numpy as np
A=np.diag(np.ones(8))
nzc=[[4],[2,5,7],[1,4],[6],[0,2],[1,7],[3],[1,5]]
for i in range(len(nzc)):
for j in nzc[i]:
A[i,j]=1
# define the Result queue
R = ["C"]*A.shape[0]
def getDegree(Graph):
"""
find the degree of each node. That is the number
of neighbours or connections.
(number of non-zero elements) in each row minus 1.
Graph is a Cubic Matrix.
"""
degree = [0]*Graph.shape[0]
for row in range(Graph.shape[0]):
degree[row] = len(np.flatnonzero(Graph[row]))-1
return degree
# find the starting point, the parent
degree = getDegree(A)
adj = getAdjcncy(A)
degree2=degree[::]
adj2 = adj[::]
digar=np.array(degree2)
pivots = list(np.where(digar == digar.min())[0])
def main_loop2(deg,start, adj,R):
degcp=deg[:]
digar=np.array(deg)
# use np.where here to get indecies of minimums
if start not in R:
R.append(start)
degcp.pop(start)
if start in pivots:
pivots.pop(start)
print "p: ", pivots
Q=adj[start]
for idx, item in enumerate(Q):
if item not in R:
R.append(item)
print "R", R
print "starts", adj[R[-1]]
Q=adj[R[-1]]
if set(Q).issubset(set(R)) and len(R) < len(degcp) :
print "will now look for new pivot"
p = pivots[0]
pivots.pop(0)
print "pivots", pivots
print "starting with" , p
main_loop2(deg,p,adj,R)
return 'this is never reached'
elif len(R) < len(degcp):
main_loop2(deg,R[-1],adj,R)
return 'wrong'
else:
print "will return R"
print type(R)
return R
inl=[]
Res = main_loop2(degree2,0, adj,inl)
print(Res)
Degrees: [1, 3, 2, 1, 2, 2, 1, 2]
0
p: [3, 6]
R [0, 4]
starts [0, 2]
R 2 degcp 7
R [0, 4, 2]
starts [1, 4]
R 3 degcp 8
R [0, 4, 2, 1]
starts [2, 5, 7]
R 4 degcp 8
R [0, 4, 2, 1, 5]
R [0, 4, 2, 1, 5, 7]
starts [1, 5]
will now look for new pivot
pivots [6]
starting with 3
R [0, 4, 2, 1, 5, 7, 3, 6]
starts [3]
will return R
<type 'list'>
wrong
所以问题是:
为什么函数在递归的所有周期都正常工作,但在最后一个,
它返回值wrong
?
输出显示最后else
只到达一次,但是没有返回列表,我在这里很无奈。
如果有人对此有所了解,我将不胜感激。
我发现了另一个问题about python and recursion,当我在那里应用解决方案时,我的代码正常运行!
所以,而不是每main_loop2(deg,R[-1],adj,R)
我写retrun main_loop2(deg,R[-1],adj,R)
,现在输出是:
... snip ...
R [0, 4, 2, 1, 5, 7]
starts [1, 5]
will now look for new pivot
pivots [6]
starting with 3
R [0, 4, 2, 1, 5, 7, 3, 6]
starts [3]
will return R
<type 'list'>
[0, 4, 2, 1, 5, 7, 3, 6]
答案 0 :(得分:3)
递归调用的最高级别进入此处:
elif len(R) < len(degcp):
main_loop2(deg,R[-1],adj,R)
return 'wrong'
无论在main_loop2
的递归调用中进一步发生什么都无关紧要;当它退出时,它将执行return 'wrong'
语句。你需要实际返回最里面的调用产生的值,一直回到顶层 - 它不会为你神奇地发生。
你的意思是return main_loop2(...)
吗?