Go Back > Math Stuff > Computer Science & Computational Number Theory > PARI/GP

Thread Tools
Old 2020-08-01, 03:23   #12
Romulan Interpreter
LaurV's Avatar
Jun 2011

2·32·5·107 Posts

Originally Posted by R. Gerbicz View Post
Good question, it is not binary search,
Methink is some Brent/Newton variation (it computes the tangents, and their Ox intersection to get next point). You may force the "abort" by playing with real precision defaults.

Edit: yep, the manual says it uses Brent (draw a secant from a to b, it intersects Ox, that is the new point, it matched with your output, well, Brent Method is a bit more complex, but that is the idea, and it should be very easy to implement a Brent(function, a, b, epsilon) to work as intended, give me some minutes for a recursive version...).

Last fiddled with by LaurV on 2020-08-01 at 03:50
LaurV is online now   Reply With Quote
Old 2020-08-01, 10:03   #13
R. Gerbicz
R. Gerbicz's Avatar
"Robert Gerbicz"
Oct 2005

148510 Posts

Originally Posted by LaurV View Post
Edit: yep, the manual says it uses Brent (draw a secant from a to b, it intersects Ox, that is the new point, it matched with your output, well,
Ok, but for f(x)=x^3 it is weaker than the binary search. Just try this:
cnt=0;solve(x=-1,2,cnt+=1;print(cnt" "x);x^3)
So it is doing at most 259 iterations.
R. Gerbicz is offline   Reply With Quote
Old 2020-08-16, 11:02   #14
JeppeSN's Avatar
Jan 2016

23×3×7 Posts

I thought the problem would go away if you shifted away from zero (where the floating point number representation can shift almost arbitrarily), but it still cannot do any of:
solve(x=-1, 2, x^3)
solve(x=-1+0.1, 2+0.1, (x-0.1)^3) - 0.1
solve(x=-1+0.1, 2+0.1, print(x);(x-0.1)^3) - 0.1
with usual realprecision default. /JeppeSN
JeppeSN is offline   Reply With Quote

Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
How to solve: k(b^m)-z=n*d. ? JM Montolio A Miscellaneous Math 18 2018-03-09 15:32
The FBI wants YOU to help solve a murder ixfd64 Puzzles 4 2011-03-30 12:25
Solve for mod function flouran Miscellaneous Math 23 2009-01-04 20:03
An Equation to Solve davar55 Puzzles 3 2008-10-09 00:35
Solve this equation davar55 Puzzles 52 2007-06-26 21:41

All times are UTC. The time now is 05:37.

Sat Jul 24 05:37:55 UTC 2021 up 1 day, 6 mins, 1 user, load averages: 0.80, 1.04, 1.15

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.