# Revision history [back]

### Help! I have a problem with lists!

Hello!

I am a real beginner in Sage, I have just started th use it. In fact this is my first programing language, so I have some difficulties with it... Now I needed a command, which determins all the k-element subset of [1,2,...,N]. Since I don't found a command like this, I decided to write a program... :-) And now I simple don't understand while my program doesn't work corrrectly! Could you explain me? It is a bit longish, so sorry for this.

def eve(A,N): #the largest elem in the list A which can be increased by 1, such that the resulting list contains only different elements less than N. Originally A should contain different elements in increasing order.

ev=len(A)-1

while A[ev]==ev+N-len(A):
ev=ev-1

return ev


def rakovetkezo(A,N): # Increases the eve(A,N)nt element by 1, and all the other elements after this element are succesive natural numbers

Q=A
ev=eve(Q,N)
x=Q[ev]

for i in range(ev,len(Q)):
Q[i]=x+i-ev+1

return Q


def reszhalmazok(N,k): #It should (but it doesn't) return the k-element subset of [1,2,...,N]

X=range(k)

B=[range(k)]

ev=eve(X,N)

while ev!=-1:

X=rakovetkezo(X,N)
B.append(X)

ev=eve(X,N)

return B


Now reszhalmazok(5,3) should return [[0,1,2], [0,1,3],...] but it returns something completely different, aaand I don't see why, and how could be improve it?

Katika

 2 Fixed some formatting issues. Mike Hansen 4068 ●24 ●48 ●89

### Help! I have a problem with lists!

Hello!

I am a real beginner in Sage, I have just started th use it. In fact this is my first programing language, so I have some difficulties with it... Now I needed a command, which determins all the k-element subset of [1,2,...,N]. Since I don't found a command like this, I decided to write a program... :-) And now I simple don't understand while my program doesn't work corrrectly! Could you explain me? It is a bit longish, so sorry for this.

def    eve(A,N):                                                                                                 #the eve(A,N):
"""
the largest elem in the list A which can
be increased by 1, such that the resulting list contains only
different elements less than N. Originally
A should contain different elements in increasing order.  ev=len(A)-1

order.
"""
ev = len(A)-1
while A[ev]==ev+N-len(A):
ev=ev-1

A[ev] == ev+N-len(A):
ev=ev-1
return ev
ev

def rakovetkezo(A,N):            # rakovetkezo(A,N):
"""
Increases the eve(A,N)nt element by 1, and all the other elements  after this element are  succesive  natural numbers    numbers
"""
Q=A
ev=eve(Q,N)
x=Q[ev]

x=Q[ev]
for i in range(ev,len(Q)):
Q[i]=x+i-ev+1
return Q
Q

def reszhalmazok(N,k):      #It reszhalmazok(N,k):
"""
It should (but it doesn't) return the k-element  subset of [1,2,...,N] [1,2,...,N]
"""
X=range(k)
B=[range(k)]
ev=eve(X,N)
while ev!=-1:

ev != -1:
X=rakovetkezo(X,N)
B.append(X)

ev=eve(X,N)

ev = eve(X,N)
return B
Now reszhalmazok(5,3) reszhalmazok(5,3) should return [[0,1,2], [0,1,3],...] [0,1,3],...] but it returns something completely different, aaand I don't see why, and how could be improve it? Katika 


 3 Added some more tags updated 2010-10-16 14:28:04 +0200 Mike Hansen 4068 ●24 ●48 ●89 Help! I have a problem with lists! Hello! I am a real beginner in Sage, I have just started th use it. In fact this is my first programing language, so I have some difficulties with it... Now I needed a command, which determins all the k-element subset of [1,2,...,N]. Since I don't found a command like this, I decided to write a program... :-) And now I simple don't understand while my program doesn't work corrrectly! Could you explain me? It is a bit longish, so sorry for this. def eve(A,N): """ the largest elem in the list A which can be increased by 1, such that the resulting list contains only different elements less than N. Originally A should contain different elements in increasing order. """ ev = len(A)-1 while A[ev] == ev+N-len(A): ev=ev-1 return ev def rakovetkezo(A,N): """ Increases the eve(A,N)nt element by 1, and all the other elements after this element are succesive natural numbers """ Q=A ev=eve(Q,N) x=Q[ev] for i in range(ev,len(Q)): Q[i]=x+i-ev+1 return Q def reszhalmazok(N,k): """ It should (but it doesn't) return the k-element subset of [1,2,...,N] """ X=range(k) B=[range(k)] ev=eve(X,N) while ev != -1: X=rakovetkezo(X,N) B.append(X) ev = eve(X,N) return B Now reszhalmazok(5,3) should return [[0,1,2], [0,1,3],...] but it returns something completely different, aaand I don't see why, and how could be improve it? Katika 


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