Hi Christoph,
Am 01.07.19 um 13:41 schrieb Christoph Hertzberg:
> Essentially, the questions are
> * Do you need min/max-behavior which propagates NaNs or numbers?
> * Do you want to control that behavior per function or per compilation unit?
> * In the above-mentioned bug, I suggested adding an optional template
parameter to each min/max function. Do you you see any drawbacks, or do you have
alternative ideas?
Speaking for myself there's no need to act on this problem.
I'd like to remark that in my numeric NaNs always signals a problem
with my code and I'm setting traps to be on the safe side, at least during
development.
In case you are interested you can add the attached example to the
documentation.
Note, setting the traps allows the debugger to reveal the problem.
> And then there is a more general question about Eigen's behavior regarding
fast-math in general:
> http://eigen.tuxfamily.org/bz/show_bug.cgi?id=1687
> i.e., EIGEN_FAST_MATH is currently enabled by default which is probably
barely noticed since it mostly influences behavior of SIMD-math for calculating
sine and cosine of arrays.
> Some more general questions regarding that:
> * Does anyone actually rely on being able to disable EIGEN_FAST_MATH?
I'm not relying on 'disable EIGEN_FAST_MATH?', however I do see tweaks of the
FP-arithmetic in the final
result. E.g. FMA results in significantly better results.
> * Would anyone like to have more control over fast-math behavior? (setting
ERRNO, always ignoring NaN/infinities/denormals, ...)
I set the appropriate traps myself and I hope that Eigen doesn't overwrite them.
Concerning the fast-math discussion, am I'm right in assuming that it Eigen
does not
decrease the accuracy of interval arithmetic?
Best regards,
Peter
#include <iostream>
#include <Eigen/Core>
// g++ -O3 -DEIGEN_FAST_MATH -ffast-math -I ~/RG/Eigen/eigen-stable NaN.C -o NaN && ./NaN
// g++ -g -I ~/RG/Eigen/eigen-stable NaN.C -o NaN && ./NaN
// -------------------------------
#include <signal.h>
#include <fenv.h>
void trapfpe(void)
{
feenableexcept(FE_INVALID); // FE_INVALID needed to trap nan
//feenableexcept(FE_INVALID|FE_DIVBYZERO|FE_OVERFLOW);
}
// -------------------------------
int main()
{
/// setting NaN trap
trapfpe();
Eigen::ArrayXd arr(6);
arr << 2,2, 0.0/0.0, 0.0/0.0, 1, 1;
std::cout << arr.transpose() << "\nmaxCoeff() = " << arr.maxCoeff() << std::endl;
}
