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[math] implement genvector custom axis rotation #18462

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[math] implement genvector custom axis rotation #18462

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f5d6fe6
[math] implement genvector custom axis rotation
ferdymercury Apr 22, 2025
4d77577
[skip-ci] alignment
ferdymercury Apr 22, 2025
57964be
[math] wrap angle into 2pi
ferdymercury Apr 23, 2025
24cc921
[math] for consistency, do the same check in TRotation
ferdymercury Apr 23, 2025
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44 changes: 41 additions & 3 deletions math/genvector/inc/Math/GenVector/VectorUtil.h
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Original file line number Diff line number Diff line change
Expand Up @@ -279,11 +279,13 @@ namespace ROOT {
/**
rotation along X axis for a generic vector by an Angle alpha
returning a new vector.
The only pre requisite on the Vector is that it has to implement the X() , Y() and Z()
The only pre requisite on the Vector is that it has to implement the X(), Y() and Z()
and SetXYZ methods.
*/
template <class Vector>
Vector RotateX(const Vector & v, double alpha) {
if (std::fmod(alpha, 2*M_PI ) == 0.)
return v;
using std::sin;
double sina = sin(alpha);
using std::cos;
Expand All @@ -298,11 +300,13 @@ namespace ROOT {
/**
rotation along Y axis for a generic vector by an Angle alpha
returning a new vector.
The only pre requisite on the Vector is that it has to implement the X() , Y() and Z()
The only pre requisite on the Vector is that it has to implement the X(), Y() and Z()
and SetXYZ methods.
*/
template <class Vector>
Vector RotateY(const Vector & v, double alpha) {
if (std::fmod(alpha, 2*M_PI ) == 0.)
return v;
using std::sin;
double sina = sin(alpha);
using std::cos;
Expand All @@ -317,11 +321,13 @@ namespace ROOT {
/**
rotation along Z axis for a generic vector by an Angle alpha
returning a new vector.
The only pre requisite on the Vector is that it has to implement the X() , Y() and Z()
The only pre requisite on the Vector is that it has to implement the X(), Y() and Z()
and SetXYZ methods.
*/
template <class Vector>
Vector RotateZ(const Vector & v, double alpha) {
if (std::fmod(alpha, 2*M_PI ) == 0.)
return v;
using std::sin;
double sina = sin(alpha);
using std::cos;
Expand All @@ -332,6 +338,38 @@ namespace ROOT {
vrot.SetXYZ(x2, y2, v.Z());
return vrot;
}

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why not implementing an access operator in the Rotation3D class instead?

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see e.g. #18480

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Thanks Monica for the swift review.
Wrt using the Rotation3D class: It's maybe a bit less efficient to define an AxisAngle, then a TRotation3D, and finally calling Rotate, than doing the direct multiplication?

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You have a point. However, I agree with the author of the forum post you mentioned, it's counter-intuitive that a TRotation3D does not work with Rotate...

/**
rotation along a custom axis for a generic vector by an Angle alpha (in rad)
returning a new vector.
The only pre requisite on the Vector is that it has to implement the X(), Y() and Z()
and SetXYZ methods.
*/
template <class Vector>
Vector Rotate(const Vector & v, double alpha, const Vector & axis) {
if (std::fmod(alpha, 2*M_PI ) == 0.)
return v;
const double ll = std::sqrt(axis.X()*axis.X() + axis.Y()*axis.Y() + axis.Z()*axis.Z());
if (ll == 0.)
GenVector::Throw("Axis Vector has zero magnitude");
const double sa = std::sin(alpha);
const double ca = std::cos(alpha);
const double dx = axis.X()/ll;
const double dy = axis.Y()/ll;
const double dz = axis.Z()/ll;
const double rot00 = (1-ca)*dx*dx+ca , rot01 = (1-ca)*dx*dy-sa*dz, rot02 = (1-ca)*dx*dz+sa*dy,
rot10 = (1-ca)*dy*dx+sa*dz, rot11 = (1-ca)*dy*dy+ca , rot12 = (1-ca)*dy*dz-sa*dx,
rot20 = (1-ca)*dz*dx-sa*dy, rot21 = (1-ca)*dz*dy+sa*dx, rot22 = (1-ca)*dz*dz+ca;
const double xX = v.X();
const double yY = v.Y();
const double zZ = v.Z();
const double x2 = rot00*xX + rot01*yY + rot02*zZ;
const double y2 = rot10*xX + rot11*yY + rot12*zZ;
const double z2 = rot20*xX + rot21*yY + rot22*zZ;
Vector vrot;
vrot.SetXYZ(x2,y2,z2);
return vrot;
}


/**
Expand Down
3 changes: 2 additions & 1 deletion math/physics/src/TRotation.cxx
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Expand Up @@ -185,6 +185,7 @@ TVector3 class:
#include "TRotation.h"
#include "TMath.h"
#include "TQuaternion.h"
#include <cmath>

ClassImp(TRotation);

Expand Down Expand Up @@ -323,7 +324,7 @@ TRotation::TRotation(const TQuaternion & Q) {
/// Rotate along an axis.

TRotation & TRotation::Rotate(Double_t a, const TVector3& axis) {
if (a != 0.0) {
if (std::fmod(a, 2*M_PI) != 0.) {
Double_t ll = axis.Mag();
if (ll == 0.0) {
Warning("Rotate(angle,axis)"," zero axis");
Expand Down
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