On Wed, Jun 3, 2009 at 10:51 AM, moky <moky.m...@gmail.com> wrote:
>
> Hello
>
>
> I would like to define a constant function in a script.
>
>
>
> I have the following in the terminal :
>
>
> =====================================================
>
> 19:43:28 ~ >$ sage
> ----------------------------------------------------------------------
> | Sage Version 4.0, Release Date: 2009-05-29 |
> | Type notebook() for the GUI, and license() for information. |
> ----------------------------------------------------------------------
> sage: var('x')
> x
> sage: f(x)= 8
> sage: print f.derivative()
> x |--> 0
> sage: type(f)
> <type 'sage.symbolic.expression.Expression'>
>
> =====================================================
>
> That seems quite good.
>
>
>
> But the following produce the error
> SyntaxError: can't assign to function call
> =====================================
>
> #! /usr/bin/sage -python
> # -*- coding: utf8 -*-
>
> from sage.all import *
>
> var('x')
> f(x)= 8
> print f.derivative()
>
> ===============================
>
> If I write f=8 instead of f(x)=8, I gat the following :
> File "./sagess.py", line 8, in <module>
> print f.derivative()
> AttributeError: 'int' object has no attribute 'derivative'
>
>
> The difference between the same lines in the terminal and in a very
> simple script seems strange to me.
>
>
> I'm using the workaround :
> var('x')
> f = 8+x-x
>
> But ... hum ... seriously ?
> ;)
Write
f = SR(8)
rather than f = 8+x-x.
That explicitly makes 8 as an element of the symbolic ring.
>
>
> Any better idea ?
>
> Thanks a lot
> Laurent
>
>
> >
>
--
William Stein
Associate Professor of Mathematics
University of Washington
http://wstein.org
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