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numerically more stable 

avoids division by zero
This commit is contained in:
Martin Diehl 2019-04-06 11:23:31 +02:00
parent bfb6ad557f
commit 1aed224c3b
1 changed files with 3 additions and 3 deletions
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6
src/rotations.f90
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@ -777,12 +777,12 @@ pure function qu2ax(qu) result(ax)
real(pReal) :: omega, s
omega = 2.0 * acos(math_clip(qu%w,-1.0_pReal,1.0_pReal))
! if the angle equals zero, then we return the rotation axis as [001]
if (dEq0(omega)) then
ax = [ 0.0, 0.0, 1.0, 0.0 ]
if (dEq0(sqrt(qu%x**2+qu%y**2+qu%z**2))) then
ax = [ 0.0_pReal, 0.0_pReal, 1.0_pReal, 0.0_pReal ]
elseif (dNeq0(qu%w)) then
s = sign(1.0_pReal,qu%w)/sqrt(qu%x**2+qu%y**2+qu%z**2)
omega = 2.0_pReal * acos(math_clip(qu%w,-1.0_pReal,1.0_pReal))
ax = [ qu%x*s, qu%y*s, qu%z*s, omega ]
else
ax = [ qu%x, qu%y, qu%z, PI ]