[sage-devel] Re: symbolic variable treated as sqrt(-1) when it shouldn't be
On Sep 3, 2:28 pm, William Stein wst...@gmail.com wrote:
Hi Sage-Devel,
What do you think of this:
sage: var('x, i')
sage: solve(x^2 + i == 0, x)
[x == -sqrt(-I), x == sqrt(-I)]
Basically, I make a purely symbolic variable which I happen to call
i, and it gets treated somewhere (presumably in Maxima) as if it
were sqrt(-1).
Here is another instance of this:
sage: var('i')
i
sage: a = i^2
sage: a
i^2
sage: a.simplify_full()
-1
So Ginac treats things fine, but our use of Maxima messes it up.
This came up for me just now when doing some symbolic calculation with
a quaternion algebra where the generators are called i,j,k, and this
i has nothing to do with sqrt(-1).
Thoughts?
William
I see your point. I guess to me it's another instance of the should
x be predefined question - on the whole, it's better to make this
available. It is also annoying when doing [f(i) for i in indexset],
but unless we can come up with another way to represent this, it will
be hard to do things with complexes very easily. Luckily for me, I
don't usually need that, but others may very often. Does this happen
with 'e' as well, or is that defined as a constant rather than a
variable? It seems like both are symbolic.expression.Expression.
What do the other major systems do with this - do they insist on sqrt
(-1) or CC(i) or something like that? If everyone expects this coming
in, it is an argument for it - not decisive, but a significant
argument.
- kcrisman
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[sage-devel] Re: symbolic variable treated as sqrt(-1) when it shouldn't be
On Sep 3, 2009, at 12:49 PM, kcrisman wrote:
On Sep 3, 2:28 pm, William Stein wst...@gmail.com wrote:
Hi Sage-Devel,
What do you think of this:
sage: var('x, i')
sage: solve(x^2 + i == 0, x)
[x == -sqrt(-I), x == sqrt(-I)]
Basically, I make a purely symbolic variable which I happen to call
i, and it gets treated somewhere (presumably in Maxima) as if it
were sqrt(-1).
Here is another instance of this:
sage: var('i')
i
sage: a = i^2
sage: a
i^2
sage: a.simplify_full()
-1
So Ginac treats things fine, but our use of Maxima messes it up.
This came up for me just now when doing some symbolic calculation
with
a quaternion algebra where the generators are called i,j,k, and
this
i has nothing to do with sqrt(-1).
Thoughts?
William
I see your point. I guess to me it's another instance of the should
x be predefined question - on the whole, it's better to make this
available.
I think my email must have not been clear. I think it's an instance
of a *HUGE BUG* in Sage. No more, no less.It's a bug, because
irregardless of anything being predefined, it makes no sense that
simplifying via *maxima* would just happen to decide that the formal
variable i is sqrt(-1), even though it isn't with Ginac.
William
It is also annoying when doing [f(i) for i in indexset],
but unless we can come up with another way to represent this, it will
be hard to do things with complexes very easily. Luckily for me, I
don't usually need that, but others may very often. Does this happen
with 'e' as well, or is that defined as a constant rather than a
variable? It seems like both are symbolic.expression.Expression.
What do the other major systems do with this - do they insist on sqrt
(-1) or CC(i) or something like that? If everyone expects this coming
in, it is an argument for it - not decisive, but a significant
argument.
- kcrisman
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[sage-devel] Re: symbolic variable treated as sqrt(-1) when it shouldn't be
William Stein wrote: Hi Sage-Devel, What do you think of this: I think you are right that this is a huge bug in our interface to maxima. Jason -- Jason Grout --~--~-~--~~~---~--~~ To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~--~~~~--~~--~--~---
[sage-devel] Re: symbolic variable treated as sqrt(-1) when it shouldn't be
2009/9/3 Golam Mortuza Hossain gmhoss...@gmail.com:
Hi,
On Thu, Sep 3, 2009 at 5:00 PM, William A. Steinwst...@gmail.com wrote:
sage: var('i')
i
sage: a = i^2
sage: a.simplify_full()
-1
I think my email must have not been clear. I think it's an instance
of a *HUGE BUG* in Sage. No more, no less. It's a bug, because
irregardless of anything being predefined, it makes no sense that
simplifying via *maxima* would just happen to decide that the formal
variable i is sqrt(-1), even though it isn't with Ginac.
This seems to be a problem with the way Sage convert back
maxima-returned string intro SR. So Maxima is NOT doing anything
wrong.
---
sage: from sage.calculus.calculus import
symbolic_expression_from_maxima_string
sage: symbolic_expression_from_maxima_string('%i')
I
sage: symbolic_expression_from_maxima_string('i')
I
---
So as you see, we are converting both '%i' and 'i' to imaginary 'I'
Yes, that completely nails down the bug. Thanks. This is now 6882:
http://trac.sagemath.org/sage_trac/ticket/6882
William
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