Making my own special type of variable

asked 2011-05-11 13:35:18 +0200

paragon
171 ●6 ●10 ●16

updated 2011-05-12 15:21:18 +0200

Kelvin Li
503 ●5 ●12 ●17

I want to create an object that I can take formal products and sums of, and also that remembers some extra data. I'd like to use sage's symbolic tools to do it without reimplementing multiplication, etc. For example, I'd like to make a class myVar that behaves something like this:

sage: a = myVar("some data about a")
sage: b = myVar("other important stuff")
sage: p = ((a + b)^2).expand()
a^2 + 2*a*b + b^2

sage: p.operands()
[a^2, 2a*b, b^2]

sage: p.operands()[0].operands[0]
a

sage: p.operands()[0].operands[0].get_data()
"some data about a"

I've tried subclassing Expression, but it seems like whenever I try to do some sums or products it just turns my thing into an Expression and forgets that it was a myVar.

Is something like this possible in sage?

edit retag flag offensive close merge delete

Comments

I think my syntax is probably bad in the example-- I need to be more careful about the variable names, probably, but I hope it is clear what I am trying to do.

paragon ( 2011-05-11 15:16:30 +0200 )edit

add a comment

2 Answers

Sort by » oldest newest most voted

answered 2011-05-11 22:45:20 +0200

Jason Grout
3505 ●9 ●36 ●81

This is not a complete answer, but here are some useful methods of the symbolic ring and elements for retrieving wrapped python objects:

sage: a=SR(Mod(8,3))
sage: a
2
sage: type(a)
<type 'sage.symbolic.expression.Expression'>
sage: type(a.pyobject())
<type 'sage.rings.finite_rings.integer_mod.IntegerMod_int'>
sage: b=SR._force_pyobject('test')
sage: b
'test'
sage: type(b)
<type 'sage.symbolic.expression.Expression'>
sage: type(b.pyobject())
<type 'str'>

edit flag offensive delete link

Comments

This is along the lines of what I want, but if I force my object into SR, then I can't add them together because the addition is not defined for them. I want to just inherit the addition and multiplication of the Symbolic Ring somehow without reimplementing.

paragon ( 2011-05-21 17:42:26 +0200 )edit

add a comment

answered 2011-05-12 15:46:21 +0200

Volker Braun
3281 ●11 ●30 ●75

You can't solve your problem by subclassing Expression, this requires you to assign data to every expression. Whats the data associated to the Expression a+b?

Since you only want to associate something to variables, you can just use a dictionary:

sage: var('a, b')
(a, b)
mydata = { a:'foo', b:'bar' }
sage: p = ((a + b)^2).expand()
a^2 + 2*a*b + b^2
sage: p.operands()[0].operands()[0]
a
sage: mydata[_]
'foo'

edit flag offensive delete link

Comments

I have thought about using a dictionary, but it is kind of awkward when I want to pass these things into functions and between modules, and also I sometimes want variables with the same name but different data.

paragon ( 2011-05-21 17:39:44 +0200 )edit

Also, I am ok if a+b is just an Expression, I just want to be able to extract 'a' using operands() and then get a myVar object out.

paragon ( 2011-05-21 17:40:46 +0200 )edit

add a comment

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Making my own special type of variable

Comments

2 Answers

Comments

Comments

Your Answer

Question Tools

Stats

Related questions

Making my own special type of variable edit

Comments

2 Answers

Comments

Comments

Your Answer

Question Tools

Stats

Related questions

Making my own special type of variable