Re: [IMP-dev] Fwd: FixedZYZ fixed_zyz_from_rotation

[Daniel Russel <drussel@gmail.com>]

I see the problem, I'll figure out a better way to structure the  
computations.


On Jan 31, 2010, at 3:17 PM, Javier Ãngel VelÃzquez Muriel <javi@salilab.o 
rg> wrote:
> 2010/1/30 Daniel Russel <drussel@gmail.com>:
> > Check that the choice of Euler angles isn't singular near that  
> > point (each
> > choice of Euler angles has a place where it is singular, meaning very
> > different Euler angle values produce almost the same rotation).
> Yes, I think that is what is happening here, but I don't know how to  
> repair it.
> How does the
> > instability manifest itself.
> When psi is 0, then sin(psi) = 0 and you're dividing by it. Needs a
> check, that is what I did. Does it help?
>
> > I'll try to look more into it later.
> >
> >
> > On Jan 29, 2010, at 8:46 PM, Javier Ãngel VelÃzquez Muriel
> > <javi@salilab.org> wrote:
> >
> > > That function enters into numerical instability when
> > > sin_tilt_sin_psi==0, which produces psi ==0. I've tried to fixe it,
> > > and i think is correct, but now the code throws the exception. The
> > > input and output are "apart". Can anybody help me to fix it?  
> > > Anything
> > > that I missed?
> > >
> > >  double psi= std::atan2(sin_tilt_sin_psi, cos_psi_sin_tilt);
> > >  if(almost_equal(sin_tilt_sin_psi,0,1e-6)) {
> > >   double sin_tilt= 0;
> > >   double tilt= std::atan2(sin_tilt, cos_tilt);
> > >  } else {
> > >   double sin_tilt= sin_tilt_sin_psi/std::sin(psi);
> > >   double tilt= std::atan2(sin_tilt, cos_tilt);
> > >  }
> > > //  double cos_rot= cos_rot_sin_tilt/sin_tilt;
> > > //  double sin_rot= sin_rot_sin_tilt/sin_tilt;
> > > //  double rot= std::atan2(sin_rot, cos_rot);
> > >   double rot= std::atan2(sin_rot, cos_rot);
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