[sage-support] Re: A little question about mod in function definition
So it seems there are (at least!) two classes of functions; those
which accept symbolic input, like sin:
m(x)=sin(x/2)
and those which don't, such as mod. I had not realized there was such
a distinction. Thank you all.
-Alasdair
On Jul 2, 5:15 am, William Stein wrote:
> On Wed, Jul 1, 2009 at 8:52 PM, Simon King wrote:
>
> > Hi Alasdair,
>
> > On 1 Jul., 13:00, David Joyner wrote:
> >> I think the first tries to use Sage's symbolic expression machinery
> >> but the second does not.
>
> > Yes, it seems so.
>
> > Using Sage, one should always be aware that some very handy/fancy
> > syntax is only available due to the Sage preparser.
>
> > E.g., some definitions such as f(x) = sin(x) or R.=QQ[] are not
> > valid Python. But when you do this in Sage, it internally becomes
> > sage: preparse('m(x)=sin(x)')
> > '__tmp__=var("x"); m = symbolic_expression(sin(x)).function(x)'
>
> > In your first approach, you get '__tmp__=var("x"); m =
> > symbolic_expression(mod(x,Integer(10))).function(x)'
>
> > But mod(x,Integer(10)) gives an error, since x is a symbolic variable
> > and not an integer, and since "mod" is not symbolic, in contrast to
> > "sin":
> > sage: type(sin)
> >
> > sage: type(mod)
> >
>
> For the record, at some point we may want to make "mod" work with
> symbolic input.
> I.e., I don't see any reason why at some point in the future we could
> make the following make sense:
>
> sage: x = var('x')
> sage: f = mod(x, 3)
> sage: f
> Mod(x, 3)
> sage: f.subs(x=5)
> 2
>
> This is already how Mathematica works:
>
> f := Mod[x,3]; f
> Mod[x, 3]
>
> f /. x -> 5
> 2
>
> William
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[sage-support] Re: A little question about mod in function definition
On Wed, Jul 1, 2009 at 8:52 PM, Simon King wrote:
>
> Hi Alasdair,
>
> On 1 Jul., 13:00, David Joyner wrote:
>> I think the first tries to use Sage's symbolic expression machinery
>> but the second does not.
>
> Yes, it seems so.
>
> Using Sage, one should always be aware that some very handy/fancy
> syntax is only available due to the Sage preparser.
>
> E.g., some definitions such as f(x) = sin(x) or R.=QQ[] are not
> valid Python. But when you do this in Sage, it internally becomes
> sage: preparse('m(x)=sin(x)')
> '__tmp__=var("x"); m = symbolic_expression(sin(x)).function(x)'
>
> In your first approach, you get '__tmp__=var("x"); m =
> symbolic_expression(mod(x,Integer(10))).function(x)'
>
> But mod(x,Integer(10)) gives an error, since x is a symbolic variable
> and not an integer, and since "mod" is not symbolic, in contrast to
> "sin":
> sage: type(sin)
>
> sage: type(mod)
>
>
For the record, at some point we may want to make "mod" work with
symbolic input.
I.e., I don't see any reason why at some point in the future we could
make the following make sense:
sage: x = var('x')
sage: f = mod(x, 3)
sage: f
Mod(x, 3)
sage: f.subs(x=5)
2
This is already how Mathematica works:
f := Mod[x,3]; f
Mod[x, 3]
f /. x -> 5
2
William
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[sage-support] Re: A little question about mod in function definition
Hi Alasdair,
On 1 Jul., 13:00, David Joyner wrote:
> I think the first tries to use Sage's symbolic expression machinery
> but the second does not.
Yes, it seems so.
Using Sage, one should always be aware that some very handy/fancy
syntax is only available due to the Sage preparser.
E.g., some definitions such as f(x) = sin(x) or R.=QQ[] are not
valid Python. But when you do this in Sage, it internally becomes
sage: preparse('m(x)=sin(x)')
'__tmp__=var("x"); m = symbolic_expression(sin(x)).function(x)'
In your first approach, you get '__tmp__=var("x"); m =
symbolic_expression(mod(x,Integer(10))).function(x)'
But mod(x,Integer(10)) gives an error, since x is a symbolic variable
and not an integer, and since "mod" is not symbolic, in contrast to
"sin":
sage: type(sin)
sage: type(mod)
Cheers,
Simon
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[sage-support] Re: A little question about mod in function definition
On Wed, Jul 1, 2009 at 4:43 AM, Alasdair wrote: > > Of these two examples: > > m(x)=mod(x,10) > > m=lambda x:mod(x,10) > > The first returns an error "unable to convert x (=x) to an integer". > Can anyone explain what's going on here? I think the first tries to use Sage's symbolic expression machinery but the second does not. > > Thanks, > Alasdair > > > --~--~-~--~~~---~--~~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~--~~~~--~~--~--~---
[sage-support] Re: A little question about mod in function definition
You should define a Python function def m(x): return mod(x,10) Kwankyu --~--~-~--~~~---~--~~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~--~~~~--~~--~--~---
