On Fri, Sep 19, 2008 at 6:54 AM, Alex Raichev <[EMAIL PROTECTED]> wrote:
>
> Hey all:
>
> I'm back with a follow up question on the topic of substitution in
> Sage. How can i work the following example? I have an expression
> that involves the derivative of a function, and into that expression i
> want to substitute the value of the derivative. Simple, eh? I tried
> Mike's ** trick and variations thereof, but that doesn't seem to work:
>
> sage: var('x,y')
> (x, y)
> sage: f= function('y',x)
> sage: g= diff(f,x)
> sage: h= diff(f^2,x)
> sage: print h
>
> d
> 2 y(x) (-- (y(x)))
> dx
>
> sage: print h.substitute(**{str(g):cos(x)})
Use:
sage: h.subs_expr(g == cos(x))
2*cos(x)*y(x)
I think this subs, subs_expr and substitute is very confusing in Sage,
at least to me.
Ondrej
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