Re: [sage-devel] Re: Questions about Solve
On Tue, Sep 13, 2011 at 10:48 AM, kcrisman kcris...@gmail.com wrote: Personally, I'm in favor of deprecating the solve(eq, x,y) or solve(list of equations, x,y,z) syntax, and would prefer that the variables be specified as a list: Backwards-incompatible, hence fodder for the mythical Sage 5.0 ... (Aside, that has nothing to do with this particular solve issue.) We deprecate after one year. I think deprecation should have nothing to do with sage 5.0. The policy, which we agreed on long ago is deprecation after one year (minimum), except when there is a compelling argument otherwise (e.g., combinat's pickles). -- William solve(eq, [x,y]) or solve(list of equations, [x,y,z]) Though I should point out, in fairness, that Maxima requires this - see http://maxima.sourceforge.net/docs/manual/en/maxima_20.html#IDX850 - so maybe we were wrong. P.S. I wish we had keyword-only arguments (http://www.python.org/dev/peps/pep-3102/), so that we could clearly Huh, that is interesting. -- 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 URL: http://www.sagemath.org -- William Stein Professor of Mathematics University of Washington http://wstein.org -- 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 URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
Backwards-incompatible, hence fodder for the mythical Sage 5.0 ... We deprecate after one year. I think deprecation should have nothing to do with sage 5.0. The policy, which we agreed on long ago is Sometimes we've talked about 1 year + next (major) version. My point was that 5.0 seems to eternally be one year off :) -- 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 URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
On Sep 13, 12:08 pm, Pong wypon...@gmail.com wrote:
y,z=var('y,z'); solve(6*x + 10*y + 15*z ==1,x,y,z) gives
([{x: -5/3*y - 5/2*z + 1/6}], [1])
So wacky. Definitely a bug, needless to say.
([x == -y + 3], [1])
My questions are:
1) Why the notation are different in the 2 and 3-variable case? One
gives x: and the other x==
Well, you are asking for solutions to both x *and* y, but the solve is
really designed to solve one in terms of the other(s). I just think
no one has pointed out this weirdness before. So you are using it in
a way it wasn't intended. I'm not sure whether we should add the
use, or have a warning, or both, or neither, or documentation, or...
2) What the [1] in both cases stand for ?
Compare:
sage: a = x+y==3
sage: type(a)
type 'sage.symbolic.expression.Expression'
sage: a.solve(x,y)
([x == -y + 3], [1])
sage: a.solve(x,False)
[x == -y + 3]
sage: a.solve(x,True)
([x == -y + 3], [1])
So we are giving a non-False input to the second argument (whether we
should get multiplicities) and so we get a multiplicity of 1. Which
doesn't really make sense anyway.
Maybe we should put in a check for the expression having more than one
variable before we send it to a.solve(), or maybe it just needs that
long-awaited rewrite... see http://trac.sagemath.org/sage_trac/wiki/symbolics
for some issues with solve.
3) In order to get the parameters appear in the solution, one need to
add a redundant equation. Shall we improve on that?
e.g.
solve([x+y==3,2*x+2*y==6],x,y)
[[x == -r1 + 3, y == r1]]
I think this is because when you do that, now the input is multiple,
and instead of doing Expression.solve(), it does the main solve()
routine, which deals with this.
Thoughts from others who care about solve? I'm not quite sure what
the best solution is. The easiest one is making really big letters in
the documentation that say don't do this and trying to catch these
cases.
- kcrisman
--
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
URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
On Tuesday, September 13, 2011 9:34:13 AM UTC-7, kcrisman wrote:
On Sep 13, 12:08 pm, Pong wypo...@gmail.com wrote:
y,z=var('y,z'); solve(6*x + 10*y + 15*z ==1,x,y,z) gives
([{x: -5/3*y - 5/2*z + 1/6}], [1])
So wacky. Definitely a bug, needless to say.
Yes, a bug.
([x == -y + 3], [1])
My questions are:
1) Why the notation are different in the 2 and 3-variable case? One
gives x: and the other x==
Well, you are asking for solutions to both x *and* y, but the solve is
really designed to solve one in terms of the other(s). I just think
no one has pointed out this weirdness before. So you are using it in
a way it wasn't intended. I'm not sure whether we should add the
use, or have a warning, or both, or neither, or documentation, or...
The documentation is clearly wrong: it says that it accepts a list of
variables to solve for, but it may really only use the first of these as a
variable, turning the others into other arguments. That is (and this is
repeating some of what kcrisman said), when you pass a single expression
(like 6*x + 10*y + 15*z ==1) to solve, it calls the method solve from
sage/symbolic/expression.pyx. The arguments for this are
(self, x, multiplicities=False, solution_dict=False,
explicit_solutions=False, to_poly_solve=False)
So when you call
solve(6*x + 10*y + 15*z ==1,x,y,z)
the expression becomes self, x becomes x, y becomes multiplicities,
and z becomes solution_dict. So it thinks that you are asking for a
solution in terms of x, including multiplicities (that's the 1), and as a
dictionary.
A workaround right now: solve a system instead:
sage: solve([6*x + 10*y + 15*z ==1, 1==1],x,y,z)
[[x == -5/2*r1 - 5/3*r2 + 1/6, y == r2, z == r1]]
(r1 and r2 stand for arbitrary numbers.)
Maybe we should put in a check for the expression having more than one
variable before we send it to a.solve(), or maybe it just needs that
long-awaited rewrite... see
http://trac.sagemath.org/sage_trac/wiki/symbolics
for some issues with solve.
Some sort of check on the arguments to solve would seem important. Or we
can check whether len(args)1, and if so, make sure not to pass the 2nd,
3rd, etc. variables as keyword arguments like solution_dict. Actually, we
just shouldn't pass it to Expression.solve() in this case.
3) In order to get the parameters appear in the solution, one need to
add a redundant equation. Shall we improve on that?
e.g.
solve([x+y==3,2*x+2*y==6],x,y)
[[x == -r1 + 3, y == r1]]
I think this is because when you do that, now the input is multiple,
and instead of doing Expression.solve(), it does the main solve()
routine, which deals with this.
Thoughts from others who care about solve? I'm not quite sure what
the best solution is. The easiest one is making really big letters in
the documentation that say don't do this and trying to catch these
cases.
I like the idea of doing solve(eqn, x, y, z, ...). This should work
according to the documentation, and it's a useful thing to be able to do, so
we should try to fix it.
--
John
--
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
URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
Thanks for the reply. However, I'm not so sure about the intention
part of the comment
I got the solve(x+y==3, x,y), i.e. asking solve for more than one
variables strict from the current documentation (solve? )
except I dropped the redundant equation 2x+2y==6.
Why don't solve just call the main solve() routine? but calling
Expression.solve() instead.
I think solve(x+y==3,x,y) should give
[[x == -r1 + 3, y == r1]]
while solve(x+y==3,y,x) should give
[[y == -r2 + 3, x == r2]]
Currently these can be achieved by add a redundant equation, e.g. 1==1
to the list.
On Sep 13, 9:34 am, kcrisman kcris...@gmail.com wrote:
On Sep 13, 12:08 pm, Pong wypon...@gmail.com wrote:
y,z=var('y,z'); solve(6*x + 10*y + 15*z ==1,x,y,z) gives
([{x: -5/3*y - 5/2*z + 1/6}], [1])
So wacky. Definitely a bug, needless to say.
([x == -y + 3], [1])
My questions are:
1) Why the notation are different in the 2 and 3-variable case? One
gives x: and the other x==
Well, you are asking for solutions to both x *and* y, but the solve is
really designed to solve one in terms of the other(s). I just think
no one has pointed out this weirdness before. So you are using it in
a way it wasn't intended. I'm not sure whether we should add the
use, or have a warning, or both, or neither, or documentation, or...
2) What the [1] in both cases stand for ?
Compare:
sage: a = x+y==3
sage: type(a)
type 'sage.symbolic.expression.Expression'
sage: a.solve(x,y)
([x == -y + 3], [1])
sage: a.solve(x,False)
[x == -y + 3]
sage: a.solve(x,True)
([x == -y + 3], [1])
So we are giving a non-False input to the second argument (whether we
should get multiplicities) and so we get a multiplicity of 1. Which
doesn't really make sense anyway.
Maybe we should put in a check for the expression having more than one
variable before we send it to a.solve(), or maybe it just needs that
long-awaited rewrite... seehttp://trac.sagemath.org/sage_trac/wiki/symbolics
for some issues with solve.
3) In order to get the parameters appear in the solution, one need to
add a redundant equation. Shall we improve on that?
e.g.
solve([x+y==3,2*x+2*y==6],x,y)
[[x == -r1 + 3, y == r1]]
I think this is because when you do that, now the input is multiple,
and instead of doing Expression.solve(), it does the main solve()
routine, which deals with this.
Thoughts from others who care about solve? I'm not quite sure what
the best solution is. The easiest one is making really big letters in
the documentation that say don't do this and trying to catch these
cases.
- kcrisman
--
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
URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
On 9/13/11 12:00 PM, Pong wrote: Thanks for the reply. However, I'm not so sure about the intention part of the comment I got the solve(x+y==3, x,y), i.e. asking solve for more than one variables strict from the current documentation (solve? ) except I dropped the redundant equation 2x+2y==6. Why don't solve just call the main solve() routine? but calling Expression.solve() instead. I think solve(x+y==3,x,y) should give [[x == -r1 + 3, y == r1]] while solve(x+y==3,y,x) should give [[y == -r2 + 3, x == r2]] Currently these can be achieved by add a redundant equation, e.g. 1==1 to the list. The problem is that two different methods are used, depending on if you give one equation or multiple equations. If you give one equation, then having multiple variables is not handled correctly. Personally, I'm in favor of deprecating the solve(eq, x,y) or solve(list of equations, x,y,z) syntax, and would prefer that the variables be specified as a list: solve(eq, [x,y]) or solve(list of equations, [x,y,z]) Note that currently, solve(list of equations, [x,y,z]) works, and internally, solve(list of equations, x,y,z) is converted to solve(list of equations, (x,y,z)) anyway. Thanks, Jason P.S. I wish we had keyword-only arguments (http://www.python.org/dev/peps/pep-3102/), so that we could clearly distinguish between the variables and optional keyword parameters, but alas, we have to wait until we migrate to python3 since http://bugs.python.org/issue1745 didn't get into python 2.7. -- 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 URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
Personally, I'm in favor of deprecating the solve(eq, x,y) or solve(list of equations, x,y,z) syntax, and would prefer that the variables be specified as a list: Backwards-incompatible, hence fodder for the mythical Sage 5.0 ... solve(eq, [x,y]) or solve(list of equations, [x,y,z]) Though I should point out, in fairness, that Maxima requires this - see http://maxima.sourceforge.net/docs/manual/en/maxima_20.html#IDX850 - so maybe we were wrong. P.S. I wish we had keyword-only arguments (http://www.python.org/dev/peps/pep-3102/), so that we could clearly Huh, that is interesting. -- 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 URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
On 9/13/11 12:48 PM, kcrisman wrote: Personally, I'm in favor of deprecating the solve(eq, x,y) or solve(list of equations, x,y,z) syntax, and would prefer that the variables be specified as a list: Backwards-incompatible, hence fodder for the mythical Sage 5.0 ... the deprecation could go in now, though. solve(eq, [x,y]) or solve(list of equations, [x,y,z]) Though I should point out, in fairness, that Maxima requires this - see http://maxima.sourceforge.net/docs/manual/en/maxima_20.html#IDX850 - so maybe we were wrong. So does mathematica: http://reference.wolfram.com/mathematica/ref/Solve.html and maple: http://www.maplesoft.com/support/help/Maple/view.aspx?path=solve Jason -- 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 URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
On Tuesday, September 13, 2011 11:09:41 AM UTC-7, jason wrote: On 9/13/11 12:48 PM, kcrisman wrote: Personally, I'm in favor of deprecating the solve(eq, x,y) or solve(list of equations, x,y,z) syntax, and would prefer that the variables be specified as a list: Backwards-incompatible, hence fodder for the mythical Sage 5.0 ... the deprecation could go in now, though. Why deprecate solve(eq, x, y)? Why not just handle both solve(eq, x, y) and solve(eq, [x, y])? -- John -- 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 URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
On 9/13/11 1:30 PM, John H Palmieri wrote: On Tuesday, September 13, 2011 11:09:41 AM UTC-7, jason wrote: On 9/13/11 12:48 PM, kcrisman wrote: Personally, I'm in favor of deprecating the solve(eq, x,y) or solve(list of equations, x,y,z) syntax, and would prefer that the variables be specified as a list: Backwards-incompatible, hence fodder for the mythical Sage 5.0 ... the deprecation could go in now, though. Why deprecate solve(eq, x, y)? Why not just handle both solve(eq, x, y) and solve(eq, [x, y])? We could, just like we handle both now when we have multiple equations. Again, my personal preference is to pass the variables as a list, though. It's cleaner, in that it groups the variables together and separates them from the other solve arguments. Thanks, Jason -- 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 URL: http://www.sagemath.org
[sage-devel] Re: Questions about Solve
Okay, it turns out that this is the explanation for all the weirdness at #10750, which I hadn't bothered to figure out before. I'm updating that ticket now. -- 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 URL: http://www.sagemath.org
