Hello, On 10/26/24 5:38 PM, Dr. Mithun Bairagi wrote:
Dear all ginac lovers, I have got some wrong results when performing some simple computations using ginac.
These results are not "wrong", see below.
I have compiled and run the following c++ program using ginac-1.8.7, cln-1.3.7 (mingw64 compiler, gcc version 14.2.0, windows 10 os),
#include <ginac/ginac.h>
using namespace std; using namespace GiNaC;
int main() { cout<<(numeric(0.1)+numeric(7))<<endl; cout<<(numeric("0.01")*numeric("9"))<<endl; cout<<(numeric("0.01")*numeric("99"))<<endl; }
the above program shows the following result: 7.1000000000000000056 0.089999999999999999996 0.98999999999999999995
I have got some unwanted digits which look very ugly. I think the result should be 7.1 0.09 0.99
This result is to be expected. Remember that CLN and GiNaC (and many other systems) represent floating-point numbers in base 2, not in base 10. In such systems, each floating-point number is an exact rational number where the denominator happens to be a power of two. An exact decimal fraction (such as 7.1 = 71/10 in decimal notation) can be converted to an exact binary fraction if and only if the numerator is a power of 2. This is not the case for 71/10. On the other hand, it is the case for e.g 75/10 = 15/2, so 7.5 can be converted from string "7.5" to an internal representation exactly. As an alternative, maybe you can use rational numbers such as 71/10 throughout your computations? Apart from that, there is no solution to what you perceive as a "problem". Mankind made a big mistake settling for base 10 millennia ago. -richy.