Not sure if this is what you are after, but the following would give you
the solution:
sage: solve([e1,e2],c,a)
[[c == (d - b*e)/e, a == d/e]]
You can give n equations to solve and solve for n variables. Solve will
insert one into another automatically.
An equation has a different syntax to a substitution rule, so if you
want to substitute what is in an equation, you could write
sage: e2(a=eq1.rhs())
Not sure if there is a better way of transforming equations into
substitution rules. Perhaps the dict() function could help? You can
substitute a dictionary of variables, e.g.
sage: vars = dict(a = b + c)
sage: e2.subs(vars)
However, again the dict() arguments have a single equal sign, not a
double one as an equation. I'm sure someone can explain this much more
elegantly.
Regards,
Stan
Paul Sargent wrote:
> Hi,
>
> I keep running into a road block which I think means either I'm
> missing something simple, or I'm thinking about things the wrong way.
> I'm fairly new to sage, and CAS in general, so either is possible.
>
> Here's a simple example of what I'm doing.
>
> Lets give ourselves two symbolic equations:
>
> sage: var("a b c d e")
> sage: e1 = a == b + c
> sage: e2 = d == e * a
>
> Now, lets say I want to know what c is in terms of b, d & e. By hand
> I'd substitute e1 in e2, and then solve for c.
>
> sage: e3=e2.subs(a=b+c)
> sage: solve(e3, c)
> [c == (d - b*e)/e]
>
> All fine, but note that I had to enter e1 into the substitution
> explicitly. I've yet to find a way of substituting one symbolic
> equation into another.
>
> Is there a way?
> Where am I going wrong?
>
> Thanks
>
> Paul
>
> >
>
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