On Jun 5, 2008, at 2:34 AM, Stan wrote:
> Dear all,
>
> I would like to use Sage as an alternative to Mathematica and I am
> quite amazed about the demonstrated functionality of Sage. I just have
> a very basic problem with the way I am used to do calculations. Often,
> I define a set of equations with different variables in them, then I
> solve the equations for example for y, set some of the variables to
> prescribed values and plot y as a function of the free variable. In
> Sage, a symbolic function does not replace the variables by numbers if
> the variables have values assigned to them.
>
> Example:
>
> sage: var ('x a b')
> (x, a, b)
> sage: y=2*x^a+b
> sage: a=3;b=4
> sage: y
> 2*x^a + b
> sage: y(a=3,b=4)
> 2*x^3 + 4
>
> In the above example, y only uses the values of a and b if they are
> explicitly included in the call. This would become very tedious for a
> system of equations if I want to plot several of them with the same
> parameter values.
>
> Is there a way of formulating equations that will automatically
> evaluate if their variables have values assigned to them?
I would try something like
sage: var ('x a b')
(x, a, b)
sage: y=2*x^a+b
sage: a=3;b=4
sage: y
2*x^a + b
sage: y.subs(locals())
2*x^3 + 4
This will take all the local variables (with their names) and plug
their values in.
>
> Same example in Mathematica:
>
> In[282]:=
> y=2*x^a+b
>
> Out[282]=
> b + 2 x^a
>
> In[283]:=
> a=3;b=4;
> y
>
> Out[284]=
> 4 + 2 x^3
>
> Thanks for your help!
>
> Stan
>
> >
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/sage-support
URLs: http://www.sagemath.org
-~----------~----~----~----~------~----~------~--~---
