Hi,
While trying to compute the Golden ratio using SAGE I noticed the
following strange (to me) behavior in solve().
* This fails:
sage: var('a b phi')
(a, b, phi)
sage: solve([phi==a/b, phi==(a+b)/a], phi)
---------------------------------------------------------------------------
<type 'exceptions.ValueError'> Traceback (most recent call last)
/Users/hector/sage/<ipython console> in <module>()
/Users/hector/sage/local/lib/python2.5/site-packages/sage/calculus/equations.py
in solve(f, *args, **kwds)
1215 s = m.solve(args)
1216 except:
-> 1217 raise ValueError, "Unable to solve %s for %s"%(f, args)
1218 a = repr(s)
1219 sol_list = string_to_list_of_solutions(a)
<type 'exceptions.ValueError'>: Unable to solve [phi == a/b, phi == (b
+ a)/a] for (phi,)
* This succeeds (note the (unnecessary?) need to also solve for 'a')
sage: solve([phi==a/b, phi==(a+b)/a], phi,a)
[[phi == (1 - sqrt(5))/2, a == -2*b/(sqrt(5) + 1)], [phi == (sqrt(5) +
1)/2, a == 2*b/(sqrt(5) - 1)]]
Where the Golden ratio is phi == (sqrt(5) + 1)/2. So, am I missing
something fundamental in the way solve() works or is this a bug?
Thanks!
--
Hector
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