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asked 2014-10-31 14:56:22 -0600

Justin Hynes gravatar image

updated 2014-10-31 14:56:55 -0600

Please explain to me the difference between the two computations:

lin=2*x - y + 2.0;lin(x=-11/9,y=-4/9)
-2.22044604925031e-16

and

2*(-11/9)-(-4/9)+2.000000000000000000
0.000000000000000000

It has to be a floating point computation, and I'm interested only in the sign of the outcome, which is why the first example gives me trouble.

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Cannot confirm. In sage-6.2 this is both 0.000000000000.

rws gravatar imagerws ( 2014-11-02 01:10:44 -0600 )edit

I've had other examples. I'm new at this, so please tell me if there are specs (version, my computer or the like) where I can look for clues to fix this bug

Justin Hynes gravatar imageJustin Hynes ( 2014-11-03 04:26:53 -0600 )edit

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answered 2014-10-31 16:28:29 -0600

Justin Hynes gravatar image

I'm in 6.3. It doesn't automatically offer to update?

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answered 2014-10-31 16:12:32 -0600

FrédéricC gravatar image

In sage 6.4.rc0, they give just the same for me. Which version of sage are you using ?

sage: var('x,y')
(x, y)
sage: lin = 2 * x - y + 2.0
sage: lin.parent()
Symbolic Ring
sage: lin(x=-11/9, y=-4/9)
0.000000000000000
sage: 2 * (-11/9) - (-4/9) + 2.0
0.000000000000000
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Asked: 2014-10-31 14:56:22 -0600

Seen: 47 times

Last updated: Oct 31 '14