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Re: GMP precision problem - only getting 15 places of PI

From: mensanator
Subject: Re: GMP precision problem - only getting 15 places of PI
Date: 21 Sep 2005 00:49:47 -0700
User-agent: G2/0.2 wrote:
> I hadn't heard of the Collatz sequence before, and read up a little on
> it today. Also saw some of your correspondence on sci.math.

If you're interested, here are a couple Google groups set up for the
Collatz Conjecture.

This one's by Ernst Berg (you may have seen his name on sci.math also).

And this one's mine (somewhat quiet as I've been spending most of my
time in Ernst's group learning C and GMP).

> About the linker problem with g++ on Cygwin, I have run into it several
> times, and have discovered that re-ordering your libraries works
> sometimes. For example, on my system,
> g++ -lgmp -lgmpxx pi.cpp
> generates large numbers of "undefined reference" errors, but the
> following works just fine:
> g++ pi.cpp -lgmp -lgmpxx
> (i.e., put the source file name before the libraries). No idea why it
> works, though.

Well, I have some ideas why it doesn't work. The -lgmpxx
option tries to link to a library file named
This library does not exist on the computer I was trying
it on. I even re-ran the GMP configure and set the flag to
enable g++ support with no luck. I can't see any error in
the log file, but is not getting built. When I
first tried to use GMP I found out that the GMP makefile
depends on a bunch of other tools that are NOT installed
by default by Cygwin even when you specifically tell it to
install gcc and g++. I figured out (I think) what was missing
by much trial and error, wailing and gnashing of teeth.
So I got GMP to work with the gcc compiler. Probably I
missed something from the Cygwin install that's preventing
the gmpxx library from being built.

The good news is that on my other computer the Cygwin/GMP
install does have the library, so I must have
accidently installed it correctly.

And your program compiles and runs without error on that
computer. So I can actually do c++ now. I'll have to run my
standard Collatz benchmark (2**177149 - 1) through it to see
how it compares to C and Python.

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