CODEWITHSUNDEEP
pythonsage
Vel Crow
Vel Crow

Reputation: 25

How can I preserve the value of my parameters through a function so it can be used multiple times with its initial value?

I have just started using SAGE which is pretty close to python as I understand it, and I have come accross this problem where I'll have as a parameter of a function a matrix which I wish to use multiple times in the function with its same original function but through the different parts of the function it changes values.

I have seen in a tutorial that declaring a variable in the function as variable = list(parameter) doesnt affect the parameter or whatever is put in the parentheses. However I can't make it work.. Below is part of my program posing the problem (I can add the rest if necessary): I declare the variable determinant which has as value the result of the function my_Gauss_determinant with the variable auxmmatrix as parameter. Through the function my_Gauss_determinant the value of auxmmatrix changes but for some reason the value of mmatrix as well. How can avoid this and be able to re-use the parameter mmatrix with its original value? 

def my_Cramer_solve(mmatrix,bb):
    auxmmatrix=list(mmatrix)
    determinant=my_Gauss_determinant(auxmmatrix)
    if determinant==0:
        print 
    k=len(auxmmatrix)
       solution=[]
        for l in range(k):
            auxmmatrix1=my_replace_column(list(mmatrix),l,bb)
            determinant1=my_Gauss_determinant(auxmmatrix1)
            solution.append(determinant1/determinant0)
    return  solution

Upvotes: 2

Views: 162

Answers (2)

Samuel Lelièvre
Samuel Lelièvre

Reputation: 3453

If m is a matrix, you can copy it into mm by doing

sage: mm = m[:, :]

or

sage: mm = matrix(m)

To understand the need to copy container structures such as lists and matrices, you could read the tutorial on objects and classes in Python and Sage.

The other Sage tutorials are recommended too!

Upvotes: 0

Brendan Abel
Brendan Abel

Reputation: 37549

What you want is a copy of mmatrix. The reason list(other_list) works is because it iterates through every item in other_list to create a new list. But the mutable objects within the list aren't copied

>>> a = [{1,2}]
>>> b = list(a)
>>> b[0].add(7)
>>> a
[set([1,2,7])]

To make a complete copy, you can use copy.deepcopy to make copies of the elements within the list

>>> import copy
>>> a = [{1,2}]
>>> b = copy.deepcopy(a)
>>> b[0].add(7)
>>> a
[set([1,2])]

So if you only want to copy the list, but don't want to copy the elements within the list, you would do this

auxmmatrix = copy.copy(matrix)
determinant = my_Gauss_determinant(copy.copy(matrix))

If you want to copy the elements within the list as well, use copy.deepcopy

Upvotes: 1

Related Questions