On Wed, 13 Feb 2013, P Purkayastha wrote:
R1=RealField(20); R2=RealField(30); r=R1(sqrt(2)); R2(r*r)
I don't get it. You are trying to obtain a higher precision *after*
doing the multiplication? Then you will get an incorrect answer.
That is what I want... I want to show for example that
r1*r2+r3*r4 seems to be rational
r1*r3+r2*r4 seems not to be rational
r1*r4+r2*r3 seems not to be rational
If r1*r2+r3*r4 calculated with, say, 20 bits precision, is 5.00 when
printed with 20 bits precision, I get "too good" answer. But if I print it
with 30 bits precision, I may get something like 4.9987. That's what I
want.
Of course you can not say that some number "seems to be rational" in
general. But if r1,...,r4 are roots of monic polynomial with integer
coefficients, then every rational root of resolvent is actually integer
root. Basically I am writing about resolvent method, but will not go to
actual numerical calculations with Arbitrary Precision Real Intervals
-field or similar.
--
Jori Mäntysalo
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