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comparing Expressions in python

asked 2012-10-28 11:12:00 -0500

SLOtoSF gravatar image

updated 2015-01-14 02:43:29 -0500

FrédéricC gravatar image

Hi,

I have an Expression I want to compare:

var('x,y')
x+y == x+y

But this does not return True. Why?

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answered 2012-10-28 14:20:43 -0500

DSM gravatar image

updated 2012-10-28 14:20:55 -0500

It works for me:

sage: var("x, y")
(x, y)
sage: x+y == x+y
x + y == x + y
sage: bool(x+y == x+y)
True
sage: if (x+y == x+y):
....:     print 'yep!'
....:     
yep!

Unless you mean that you want bool to be automatically applied to every equation? Since Sage follows the convention that "False" means "I couldn't see how to prove this was true", this would mean that pretty much every equation would automatically be False from the get-go and so you couldn't do anything with it. For example, (x-2)*(x+3) == 0 would be False (x could be 9, after all).

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Thanks! I didn't know about bool(). What is the advantage of not automatically applying it?

SLOtoSF gravatar imageSLOtoSF ( 2012-10-28 16:52:23 -0500 )edit

@SLOtoSF: apparently I didn't explain well enough -- that's what my last paragraph was trying to explain. If you automatically applied it, you could never manipulate an equation because it'd be a bool instantly. No substitutions, no simplifications, nothing.

DSM gravatar imageDSM ( 2012-10-29 09:01:22 -0500 )edit

I see. Totally makes sense. Thanks.

SLOtoSF gravatar imageSLOtoSF ( 2012-10-29 09:09:26 -0500 )edit

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Asked: 2012-10-28 11:12:00 -0500

Seen: 76 times

Last updated: Oct 28 '12