/* -------------------------------------------------------------------------- *
 *                       Simbody(tm): SimTKcommon                             *
 * -------------------------------------------------------------------------- *
 * This is part of the SimTK biosimulation toolkit originating from           *
 * Simbios, the NIH National Center for Physics-Based Simulation of           *
 * Biological Structures at Stanford, funded under the NIH Roadmap for        *
 * Medical Research, grant U54 GM072970. See https://simtk.org/home/simbody.  *
 *                                                                            *
 * Portions copyright (c) 2005-14 Stanford University and the Authors.        *
 * Authors: Paul Mitiguy, Michael Sherman                                     *
 * Contributors:                                                              *
 *                                                                            *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may    *
 * not use this file except in compliance with the License. You may obtain a  *
 * copy of the License at http://www.apache.org/licenses/LICENSE-2.0.         *
 *                                                                            *
 * Unless required by applicable law or agreed to in writing, software        *
 * distributed under the License is distributed on an "AS IS" BASIS,          *
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   *
 * See the License for the specific language governing permissions and        *
 * limitations under the License.                                             *
 * -------------------------------------------------------------------------- */

/**@file
 * Implementations of non-inline methods associated with Rotation class.
 */

#include "SimTKcommon/basics.h"
#include "SimTKcommon/internal/Rotation.h"

#include <cmath>
#include <utility>

//------------------------------------------------------------------------------
namespace SimTK {


//------------------------------------------------------------------------------
// Set Rotation for ANY two-angle ij rotation sequence (i,j = X,Y,Z)
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setRotationFromTwoAnglesTwoAxes
  ( BodyOrSpaceType bodyOrSpace, 
    RealP angle1, const CoordinateAxis& axis1In, 
    RealP angle2, const CoordinateAxis& axis2In )  
{
    // Non-const CoordinateAxes in case we have to switch axes
    CoordinateAxis axis1 = axis1In;
    CoordinateAxis axis2 = axis2In;

    // If axis2 is same as axis1, efficiently calculate with a one-angle, 
    // one-axis rotation.
    if( axis1.isSameAxis(axis2) ) 
    { return setRotationFromAngleAboutAxis( angle1+angle2, axis1 ); }

    // If using a SpaceRotationSequence, switch order of axes and angles.
    if( bodyOrSpace == SpaceRotationSequence )  
    { std::swap(angle1,angle2);  std::swap(axis1,axis2); }

    // If using a reverse cyclical, negate the signs of the angles
    if( axis1.isReverseCyclical(axis2) )  
    { angle1 = -angle1; angle2 = -angle2; }

    // Calculate the sines and cosines (some hardware can do this more 
    // efficiently as one Taylor series).
    const RealP c1 = std::cos( angle1 ),  s1 = std::sin( angle1 );
    const RealP c2 = std::cos( angle2 ),  s2 = std::sin( angle2 );

    // All calculations are based on a body-fixed forward-cyclical rotation 
    // sequence.
    return setTwoAngleTwoAxesBodyFixedForwardCyclicalRotation( c1,s1,axis1,  
                                                               c2,s2,axis2 );
}


//------------------------------------------------------------------------------
// Set Rotation for ANY three-angle ijk rotation sequence where (i,j,k = X,Y,Z)
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setRotationFromThreeAnglesThreeAxes
  ( BodyOrSpaceType bodyOrSpace, 
    RealP angle1, const CoordinateAxis& axis1In, 
    RealP angle2, const CoordinateAxis& axis2, 
    RealP angle3, const CoordinateAxis& axis3In ) {

    // Non-const CoordinateAxes in case we have to switch axes.
    CoordinateAxis axis1 = axis1In;
    CoordinateAxis axis3 = axis3In;

    // If axis2 is same as axis1 or axis3, efficiently calculate with a 
    // two-angle, two-axis rotation.
    if( axis2.isSameAxis(axis1) ) 
        return setRotationFromTwoAnglesTwoAxes(bodyOrSpace, angle1+angle2, 
                                               axis1,  angle3,axis3);
    if( axis2.isSameAxis(axis3) ) 
        return setRotationFromTwoAnglesTwoAxes(bodyOrSpace, angle1,axis1,  
                                               angle2+angle3, axis3);

    // If using a SpaceRotationSequence, switch order of the axes and angles.
    if( bodyOrSpace == SpaceRotationSequence )  
    { std::swap(angle1,angle3);  std::swap(axis1,axis3); }

    // If using a reverse cyclical, negate the signs of the angles.
    if( axis1.isReverseCyclical(axis2) )  
    { angle1 = -angle1;   angle2 = -angle2;   angle3 = -angle3; }

    // Calculate the sines and cosines (some hardware can do this more 
    // efficiently as one Taylor series).
    const RealP c1 = std::cos( angle1 ),  s1 = std::sin( angle1 );
    const RealP c2 = std::cos( angle2 ),  s2 = std::sin( angle2 );
    const RealP c3 = std::cos( angle3 ),  s3 = std::sin( angle3 );

    // All calculations are based on a body-fixed rotation sequence.
    // Determine whether this is a BodyXYX or BodyXYZ type of rotation sequence.
    if( axis1.isSameAxis(axis3) )  
        setThreeAngleTwoAxesBodyFixedForwardCyclicalRotation
                                        (c1,s1,axis1, c2,s2,axis2, c3,s3);
    else                           
        setThreeAngleThreeAxesBodyFixedForwardCyclicalRotation
                                        (c1,s1,axis1, c2,s2,axis2, c3,s3,axis3);

    return *this;
}


//------------------------------------------------------------------------------
// Calculate angle for ANY X or Y or Z rotation sequence
//------------------------------------------------------------------------------
template <class P> P
Rotation_<P>::convertOneAxisRotationToOneAngle(const CoordinateAxis& axis1) const 
{
    // Get proper indices into Rotation matrix
    const CoordinateAxis axis2 = axis1.getNextAxis();
    const CoordinateAxis axis3 = axis2.getNextAxis();
    const int j = int( axis2 );
    const int k = int( axis3 );

    const Mat33P& R = asMat33();
    const RealP sinTheta = ( R[k][j] - R[j][k] ) / 2;
    const RealP cosTheta = ( R[j][j] + R[k][k] ) / 2;

    return std::atan2( sinTheta, cosTheta );
}


//------------------------------------------------------------------------------
// Calculate angles for ANY two-angle ij rotation sequence (i,j = X,Y,Z)
//------------------------------------------------------------------------------
template <class P> Vec<2,P>
Rotation_<P>::convertTwoAxesRotationToTwoAngles
  ( BodyOrSpaceType bodyOrSpace, 
    const CoordinateAxis& axis1In, 
    const CoordinateAxis& axis2In ) const 
{
    // Non-const CoordinateAxes in case we have to switch axes
    CoordinateAxis axis1 = axis1In;
    CoordinateAxis axis2 = axis2In;

    // If axis2 is same as axis1, efficiently calculate with a one-axis, 
    // one-angle method.
    if( axis1.isSameAxis(axis2) ) 
    {   const RealP theta = convertOneAxisRotationToOneAngle(axis1) / 2; 
        return Vec<2,P>(theta,theta); }

    // If using a SpaceRotationSequence, switch the order of the axes (later 
    // switch the angles).
    if( bodyOrSpace == SpaceRotationSequence )  std::swap(axis1,axis2);

    // All calculations are based on a body-fixed rotation sequence
    Vec<2,P> ans = convertTwoAxesBodyFixedRotationToTwoAngles( axis1, axis2 );

    // If using a SpaceRotationSequence, switch the angles now.
    if( bodyOrSpace == SpaceRotationSequence )  std::swap( ans[0], ans[1] );

    return ans;
}


//------------------------------------------------------------------------------
// Calculate angles for ANY 3-angle ijk rotation sequence where (i,j,k = X,Y,Z)
//------------------------------------------------------------------------------
template <class P> Vec<3,P>
Rotation_<P>::convertThreeAxesRotationToThreeAngles
  ( BodyOrSpaceType         bodyOrSpace, 
    const CoordinateAxis&   axis1In, 
    const CoordinateAxis&   axis2, 
    const CoordinateAxis&   axis3In ) const 
{
    // Non-const CoordinateAxes in case we have to switch axes.
    CoordinateAxis axis1 = axis1In;
    CoordinateAxis axis3 = axis3In;

    // If all axes are same, efficiently calculate with a one-axis, one-angle 
    // method.
    if( axis1.areAllSameAxes(axis2,axis3) ) { 
        RealP theta = convertOneAxisRotationToOneAngle(axis1) / 3;  
        return Vec3P(theta,theta,theta); 
    }

    // If axis2 is same as axis1, efficiently calculate with a two-angle, 
    // two-axis rotation.
    if( axis2.isSameAxis(axis1) ) {
        const Vec2P xz = convertTwoAxesRotationToTwoAngles
                                                    (bodyOrSpace,axis1,axis3);
        const RealP theta = xz[0] / 2;
        return Vec3P( theta, theta, xz[1] );
    }

    // If axis2 is same as axis3, efficiently calculate with a two-angle, 
    // two-axis rotation.
    if( axis2.isSameAxis(axis3) ) {
        const Vec2P xz = convertTwoAxesRotationToTwoAngles
                                                    (bodyOrSpace,axis1,axis3);
        const RealP theta = xz[1] / 2;
        return Vec3P( xz[0], theta, theta);
    }

    // If using a SpaceRotationSequence, switch the order of the axes (later 
    // switch the angles).
    if( bodyOrSpace == SpaceRotationSequence )  std::swap(axis1,axis3);

    // All calculations are based on a body-fixed rotation sequence.
    // Determine whether this is a BodyXYX or BodyXYZ type of rotation sequence.
    Vec3P ans = axis1.isSameAxis(axis3) 
        ? convertTwoAxesBodyFixedRotationToThreeAngles(axis1, axis2)
        : convertThreeAxesBodyFixedRotationToThreeAngles(axis1, axis2, axis3);

    // If using a SpaceRotationSequence, switch the angles now.
    if( bodyOrSpace == SpaceRotationSequence ) std::swap(ans[0], ans[2]);

    return ans;
}



//------------------------------------------------------------------------------
// Set Rotation ONLY for two-angle, two-axes, body-fixed, ij rotation sequence 
// where i != j.
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setTwoAngleTwoAxesBodyFixedForwardCyclicalRotation
  ( RealP cosAngle1, RealP sinAngle1, const CoordinateAxis& axis1, 
    RealP cosAngle2, RealP sinAngle2, const CoordinateAxis& axis2 ) 
{
    // Ensure this method has proper arguments
    assert( axis1.isDifferentAxis( axis2 ) );

    CoordinateAxis axis3 = axis1.getThirdAxis( axis2 );
    const int i = int( axis1 );
    const int j = int( axis2 );
    const int k = int( axis3 );

    Mat33P& R = *this;
    R[i][i] =  cosAngle2;
    R[i][j] =  0;
    R[i][k] =  sinAngle2;
    R[j][i] =  sinAngle2 * sinAngle1;
    R[j][j] =  cosAngle1;
    R[j][k] = -sinAngle1 * cosAngle2;
    R[k][i] = -sinAngle2 * cosAngle1;
    R[k][j] =  sinAngle1;
    R[k][k] =  cosAngle1 * cosAngle2;
    return *this;
}


//------------------------------------------------------------------------------
// Set Rotation ONLY for three-angle, two-axes, body-fixed, iji rotation 
// sequence where i != j.
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setThreeAngleTwoAxesBodyFixedForwardCyclicalRotation
  ( RealP cosAngle1, RealP sinAngle1, const CoordinateAxis& axis1, 
    RealP cosAngle2, RealP sinAngle2, const CoordinateAxis& axis2, 
    RealP cosAngle3, RealP sinAngle3 )  
{
    // Ensure this method has proper arguments
    assert( axis1.isDifferentAxis( axis2 ) );

    // Repeated calculations (for efficiency)
    RealP s1c3 = sinAngle1 * cosAngle3;
    RealP s3c1 = sinAngle3 * cosAngle1;
    RealP s1s3 = sinAngle1 * sinAngle3;
    RealP c1c3 = cosAngle1 * cosAngle3;

    CoordinateAxis axis3 = axis1.getThirdAxis( axis2 );
    const int i = int( axis1 );
    const int j = int( axis2 );
    const int k = int( axis3 );

    Mat33P& R =  *this;
    R[i][i] =  cosAngle2;
    R[i][j] =  sinAngle2 * sinAngle3;
    R[i][k] =  sinAngle2 * cosAngle3;
    R[j][i] =  sinAngle1 * sinAngle2;
    R[j][j] =  c1c3 - cosAngle2 * s1s3;
    R[j][k] = -s3c1 - cosAngle2 * s1c3;
    R[k][i] = -sinAngle2 * cosAngle1;
    R[k][j] =  s1c3 + cosAngle2 * s3c1;
    R[k][k] = -s1s3 + cosAngle2 * c1c3;
    return *this;
}


//------------------------------------------------------------------------------
// Set Rotation ONLY for three-angle, three-axes, body-fixed, ijk rotation 
// sequence where i != j != k.
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setThreeAngleThreeAxesBodyFixedForwardCyclicalRotation
  ( RealP cosAngle1, RealP sinAngle1, const CoordinateAxis& axis1, 
    RealP cosAngle2, RealP sinAngle2, const CoordinateAxis& axis2,
    RealP cosAngle3, RealP sinAngle3, const CoordinateAxis& axis3 ) 
{
    // Ensure this method has proper arguments
    assert( axis1.areAllDifferentAxes(axis2,axis3) );

    // Repeated calculations (for efficiency)
    RealP s1c3 = sinAngle1 * cosAngle3;
    RealP s3c1 = sinAngle3 * cosAngle1;
    RealP s1s3 = sinAngle1 * sinAngle3;
    RealP c1c3 = cosAngle1 * cosAngle3;

    const int i = int(axis1);
    const int j = int(axis2);
    const int k = int(axis3);

    Mat33P& R = *this;
    R[i][i] =  cosAngle2 * cosAngle3;
    R[i][j] = -sinAngle3 * cosAngle2;
    R[i][k] =  sinAngle2;
    R[j][i] =  s3c1 + sinAngle2 * s1c3;
    R[j][j] =  c1c3 - sinAngle2 * s1s3;
    R[j][k] = -sinAngle1 * cosAngle2;
    R[k][i] =  s1s3 - sinAngle2 * c1c3;
    R[k][j] =  s1c3 + sinAngle2 * s3c1;
    R[k][k] =  cosAngle1 * cosAngle2;
    return *this;
}


//------------------------------------------------------------------------------
// Calculate angles ONLY for a two-angle, two-axes, body-fixed, ij rotation 
// sequence where i != j.
//------------------------------------------------------------------------------
template <class P> Vec<2,P>
Rotation_<P>::convertTwoAxesBodyFixedRotationToTwoAngles
  ( const CoordinateAxis& axis1, const CoordinateAxis& axis2 ) const 
{
    // Ensure this method has proper arguments
    assert( axis1.isDifferentAxis( axis2 ) );

    CoordinateAxis axis3 = axis1.getThirdAxis(axis2);
    const int i = int(axis1);
    const int j = int(axis2);
    const int k = int(axis3);
    const Mat33P& R =  asMat33();

    // Can use either direct method (fast) or all matrix elements with the 
    // overhead of two additional square roots (possibly more accurate).
    const RealP sinTheta1Direct = R[k][j];
    const RealP signSinTheta1 = sinTheta1Direct > 0 ? RealP(1) : RealP(-1);
    const RealP sinTheta1Alternate = 
        signSinTheta1 * std::sqrt( square(R[j][i]) + square(R[j][k]) );
    const RealP sinTheta1 = ( sinTheta1Direct + sinTheta1Alternate ) / 2;

    const RealP cosTheta1Direct = R[j][j];
    const RealP signCosTheta1 = cosTheta1Direct > 0 ? RealP(1) : RealP(-1);
    const RealP cosTheta1Alternate = 
        signCosTheta1 * std::sqrt( square(R[k][i]) + square(R[k][k]) );
    const RealP cosTheta1 = ( cosTheta1Direct + cosTheta1Alternate ) / 2;

    RealP theta1 = std::atan2( sinTheta1, cosTheta1 );

    // Repeat for theta2
    const RealP sinTheta2Direct = R[i][k];
    const RealP signSinTheta2 = sinTheta2Direct > 0 ? RealP(1) : RealP(-1);
    const RealP sinTheta2Alternate = 
        signSinTheta2 * std::sqrt( square(R[j][i]) + square(R[k][i]) );
    const RealP sinTheta2 = ( sinTheta2Direct + sinTheta2Alternate ) / 2;

    const RealP cosTheta2Direct = R[i][i];
    const RealP signCosTheta2 = cosTheta2Direct > 0 ? RealP(1) : RealP(-1);
    const RealP cosTheta2Alternate = 
        signCosTheta2 * std::sqrt( square(R[j][k]) + square(R[k][k]) );
    const RealP cosTheta2 = ( cosTheta2Direct + cosTheta2Alternate ) / 2;

    RealP theta2 = std::atan2( sinTheta2, cosTheta2 );

    // If using a reverse cyclical, negate the signs of the angles
    if( axis1.isReverseCyclical(axis2) )  { theta1 = -theta1;  theta2 = -theta2; }

    // Return values have the following ranges:
    // -pi   <=  theta1  <=  +pi
    // -pi   <=  theta2  <=  +pi
    return Vec2P( theta1, theta2 );
}


//------------------------------------------------------------------------------
// Calculate angles ONLY for a three-angle, two-axes, body-fixed, iji rotation 
// sequence where i != j.
//------------------------------------------------------------------------------
template <class P> Vec<3,P>
Rotation_<P>::convertTwoAxesBodyFixedRotationToThreeAngles
  ( const CoordinateAxis& axis1, const CoordinateAxis& axis2 ) const 
{
    // Ensure this method has proper arguments.
    assert( axis1.isDifferentAxis( axis2 ) );

    CoordinateAxis axis3 = axis1.getThirdAxis( axis2 );
    const int i = int( axis1 );
    const int j = int( axis2 );
    const int k = int( axis3 );

    // Need to know if using a forward or reverse cyclical.
    RealP plusMinus = 1.0,  minusPlus = -1.0;
    if( axis1.isReverseCyclical(axis2) ) { plusMinus = -1.0,  minusPlus = 1.0; }

    // Shortcut to the elements of the rotation matrix.
    const Mat33P& R = asMat33();

    // Calculate theta2 using lots of information in the rotation matrix.
    const RealP Rsum   = std::sqrt( (  square(R[i][j]) + square(R[i][k]) 
                                     + square(R[j][i]) + square(R[k][i])) / 2 );  
    // Rsum = abs(sin(theta2)) is inherently positive.
    const RealP theta2 = std::atan2( Rsum, R[i][i] );  
    RealP theta1, theta3;

    // There is a "singularity" when sin(theta2) == 0
    if( Rsum > 4*Eps ) {
        theta1  =  std::atan2( R[j][i], minusPlus*R[k][i] );
        theta3  =  std::atan2( R[i][j], plusMinus*R[i][k] );
    }
    else if( R[i][i] > 0 ) {
        const RealP spos = plusMinus*R[k][j] + minusPlus*R[j][k];  // 2*sin(theta1 + theta3)
        const RealP cpos = R[j][j] + R[k][k];                      // 2*cos(theta1 + theta3)
        const RealP theta1PlusTheta3 = std::atan2( spos, cpos );
        theta1 = theta1PlusTheta3;  // Arbitrary split
        theta3 = 0;                 // Arbitrary split
    }
    else {
        const RealP sneg = plusMinus*R[k][j] + plusMinus*R[j][k];  // 2*sin(theta1 - theta3)
        const RealP cneg = R[j][j] - R[k][k];                      // 2*cos(theta1 - theta3)
        const RealP theta1MinusTheta3 = std::atan2( sneg, cneg );
        theta1 = theta1MinusTheta3;  // Arbitrary split
        theta3 = 0;                  // Arbitrary split
    }

    // Return values have the following ranges:
    // -pi   <=  theta1  <=  +pi
    //   0   <=  theta2  <=  +pi    (Rsum is inherently positive)
    // -pi   <=  theta3  <=  +pi
    return Vec3P( theta1, theta2, theta3 );
}


//------------------------------------------------------------------------------
// Calculate angles ONLY for a three-angle, three-axes, body-fixed, ijk rotation 
// sequence where i != j and j != k.
//------------------------------------------------------------------------------
template <class P> Vec<3,P>
Rotation_<P>::convertThreeAxesBodyFixedRotationToThreeAngles
  ( const CoordinateAxis& axis1, const CoordinateAxis& axis2, 
    const CoordinateAxis& axis3 ) const 
{
    // Ensure this method has proper arguments.
    assert( axis1.areAllDifferentAxes(axis2,axis3) );

    const int i = int(axis1);
    const int j = int(axis2);
    const int k = int(axis3);

    // Need to know if using a forward or reverse cyclical.
    RealP plusMinus = 1.0,  minusPlus = -1.0;
    if( axis1.isReverseCyclical(axis2) ) { plusMinus = -1.0,  minusPlus = 1.0; }

    // Shortcut to the elements of the rotation matrix.
    const Mat33P& R = asMat33();

    // Calculate theta2 using lots of information in the rotation matrix.
    RealP Rsum   =  std::sqrt((  square(R[i][i]) + square(R[i][j]) 
                               + square(R[j][k]) + square(R[k][k])) / 2);
    // Rsum = abs(cos(theta2)) is inherently positive.
    RealP theta2 =  std::atan2( plusMinus*R[i][k], Rsum ); 
    RealP theta1, theta3;

    // There is a "singularity" when cos(theta2) == 0
    if( Rsum > 4*Eps ) {
        theta1 =  std::atan2( minusPlus*R[j][k], R[k][k] );
        theta3 =  std::atan2( minusPlus*R[i][j], R[i][i] );
    }
    else if( plusMinus*R[i][k] > 0 ) {
        const RealP spos = R[j][i] + plusMinus*R[k][j];  // 2*sin(theta1 + plusMinus*theta3)
        const RealP cpos = R[j][j] + minusPlus*R[k][i];  // 2*cos(theta1 + plusMinus*theta3)
        const RealP theta1PlusMinusTheta3 = std::atan2( spos, cpos );
        theta1 = theta1PlusMinusTheta3;  // Arbitrary split
        theta3 = 0;                      // Arbitrary split
    }
    else {
        const RealP sneg = plusMinus*(R[k][j] + minusPlus*R[j][i]);  // 2*sin(theta1 + minusPlus*theta3)
        const RealP cneg = R[j][j] + plusMinus*R[k][i];              // 2*cos(theta1 + minusPlus*theta3)
        const RealP theta1MinusPlusTheta3 = std::atan2( sneg, cneg );
        theta1 = theta1MinusPlusTheta3;  // Arbitrary split
        theta3 = 0;                      // Arbitrary split
    }

    // Return values have the following ranges:
    // -pi   <=  theta1  <=  +pi
    // -pi/2 <=  theta2  <=  +pi/2   (Rsum is inherently positive)
    // -pi   <=  theta3  <=  +pi
    return Vec3P( theta1, theta2, theta3 );
}


//------------------------------------------------------------------------------
// Calculate R_AB by knowing one of B's unit vector expressed in A.
// Note: The other vectors are perpendicular (but somewhat arbitrarily so).
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setRotationFromOneAxis(const UnitVec3P& uveci, CoordinateAxis axisi)  
{
    // Find a unit vector that is perpendicular to uveci.
    const UnitVec3P uvecj = uveci.perp();

    // Find another unit vector that is perpendicular to both uveci and uvecj.
    const UnitVec3P uveck = UnitVec3P( cross( uveci, uvecj ) );

    // Determine which of the axes this corresponds to.
    CoordinateAxis axisj = axisi.getNextAxis();
    CoordinateAxis axisk = axisj.getNextAxis();

    // Fill in the correct elements of the Rotation matrix.
    setRotationColFromUnitVecTrustMe( int(axisi), uveci );
    setRotationColFromUnitVecTrustMe( int(axisj), uvecj );
    setRotationColFromUnitVecTrustMe( int(axisk), uveck );

    return *this;
}


//------------------------------------------------------------------------------
// Calculate A.RotationMatrix.B by knowing one of B's unit vectors expressed in 
// A and another vector that may be perpendicular. If the 2nd vector is not 
// perpendicular, no worries - we'll make it so it is perpendicular.
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setRotationFromTwoAxes
  ( const UnitVec3P& uveci, const CoordinateAxis& axisi, 
    const Vec3P& vecjApprox, const CoordinateAxis& axisjApprox ) 
{
    // Ensure vecjApprox is not a zero vector and the axes are not the same.
    RealP magnitudeOfVecjApprox = vecjApprox.normSqr();
    if( magnitudeOfVecjApprox==0  ||  axisi.isSameAxis(axisjApprox) )
      return setRotationFromOneAxis( uveci, axisi );

    // Create a unit vector that is perpendicular to both uveci and vecjApprox.
    Vec3P veck = cross( uveci, vecjApprox );

    // Make sure (a x b) is not too close to the zero vector (vectors are nearly
    // parallel). Since |a x b| = |a|*|b|*sin(theta), it is easy to determine 
    // when sin(theta) = |a x b| / (|a| * |b|) is small. In other words, 
    // sin(theta) = |a x b| / (|a| * |b|)  where |a| = 1 (since uveci is a unit 
    // vector). I use SqrtEps (which is approx 1e-8 in double) which means 
    // that the angle between the vectors is less than 1e-8 rads = 6e-7 deg.
    RealP magnitudeOfVeck = veck.normSqr();   // Magnitude of the cross product.
    if( magnitudeOfVeck < SimTK::SqrtEps * magnitudeOfVecjApprox )
        return setRotationFromOneAxis( uveci, axisi );

    // Find a unit vector that is perpendicular to both uveci and vecjApprox.
    UnitVec3P uveck = UnitVec3P( veck );

    // Compute the unit vector perpendicular to both uveci and uveck.
    UnitVec3P uvecj = UnitVec3P( cross( uveck, uveci ) );

    // Determine which of the axes this corresponds to
    CoordinateAxis axisj = axisi.getNextAxis();
    CoordinateAxis axisk = axisj.getNextAxis();

    // If axisj is axisjApprox, all is good, otherwise switch axisj and axisk 
    // and negate the k'th axis.
    if( axisj.isDifferentAxis(axisjApprox) ) {
        std::swap( axisj, axisk );
        uveck = -uveck;
    }

    // Fill in the correct elements of the Rotation matrix
    setRotationColFromUnitVecTrustMe( int(axisi), uveci );
    setRotationColFromUnitVecTrustMe( int(axisj), uvecj );
    setRotationColFromUnitVecTrustMe( int(axisk), uveck );

    return *this;
}


//------------------------------------------------------------------------------
// Set this rotation matrix from the associated quaternion. (29 flops)
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setRotationFromQuaternion( const Quaternion_<P>& q )  {
    const RealP q00=q[0]*q[0], q11=q[1]*q[1], q22=q[2]*q[2], q33=q[3]*q[3];
    const RealP q01=q[0]*q[1], q02=q[0]*q[2], q03=q[0]*q[3];
    const RealP q12=q[1]*q[2], q13=q[1]*q[3], q23=q[2]*q[3];
    const RealP q00mq11 = q00-q11, q22mq33 = q22-q33;

    Mat33P::operator=(Mat33P(q00+q11-q22-q33,  2*(q12-q03)  ,  2*(q13+q02),
                               2*(q12+q03)  ,q00mq11+q22mq33,  2*(q23-q01),
                               2*(q13-q02)  ,  2*(q23+q01)  ,q00mq11-q22mq33));
    return *this;
}


//------------------------------------------------------------------------------
// Convert this Rotation matrix to the equivalent quaternion.
//
// We use a modification of Richard Spurrier's method: Spurrier, R.A., "Comment
// on 'Singularity-Free Extraction of a Quaternion from a Direction-Cosine 
// Matrix'", J. Spacecraft and Rockets, 15(4):255, 1977. Our modification 
// avoids all but one square root and divide. In each of the four cases we 
// compute 4q[m]*q where m is the "max" element, with
//   m=0 if the trace is larger than any diagonal or
//   m=i if the i,i element is the largest diagonal and larger than the trace.
// Then when we normalize at the end the scalar 4q[m] evaporates leaving us
// with a perfectly normalized quaternion.
//
// The returned quaternion can be interpreted as a rotation angle a about a unit
// vector v=[vx vy vz] like this:    q = [ cos(a/2) sin(a/2)*v ]
// We canonicalize the returned quaternion by insisting that
// cos(a/2) >= 0, meaning that -180 < a <= 180.
//
// This takes about 40 flops.
//------------------------------------------------------------------------------
template <class P> Quaternion_<P>
Rotation_<P>::convertRotationToQuaternion() const {
    const Mat33P& R = asMat33();

    // Stores the return values [cos(theta/2), lambda1*sin(theta/2), 
    //                           lambda2*sin(theta/2), lambda3*sin(theta/2)]
    Vec4P q;

    // Check if the trace is larger than any diagonal
    const RealP tr = R.trace();
    if( tr >= R(0,0)  &&  tr >= R(1,1)  &&  tr >= R(2,2) ) {
        q[0] = 1 + tr;
        q[1] = R(2,1) - R(1,2);
        q[2] = R(0,2) - R(2,0);
        q[3] = R(1,0) - R(0,1);

    // Check if R(0,0) is largest along the diagonal
    } else if( R(0,0) >= R(1,1)  &&  R(0,0) >= R(2,2)  ) {
        q[0] = R(2,1) - R(1,2);
        q[1] = 1 - (tr - 2*R(0,0));
        q[2] = R(0,1)+R(1,0);
        q[3] = R(0,2)+R(2,0);

    // Check if R(1,1) is largest along the diagonal
    } else if( R(1,1) >= R(2,2) ) {
        q[0] = R(0,2) - R(2,0);
        q[1] = R(0,1) + R(1,0);
        q[2] = 1 - (tr - 2*R(1,1));
        q[3] = R(1,2) + R(2,1);

    // R(2,2) is largest along the diagonal
    } else {
        q[0] = R(1,0) - R(0,1);
        q[1] = R(0,2) + R(2,0);
        q[2] = R(1,2) + R(2,1);
        q[3] = 1 - (tr - 2*R(2,2));
    }
    RealP scale = q.norm();
    if( q[0] < 0 )  scale = -scale;   // canonicalize
    return Quaternion_<P>(q/scale, true); // prevent re-normalization
}



//------------------------------------------------------------------------------
// Determine whether "this" Rotation matrix is nearly identical to the one 
// passed in (R) within a specified "pointing angle error".  If "this" and "R" 
// are nearly identical, transpose(this) * R = closeToIdentity matrix. After 
// finding the equivalent angle-axis for closeToIdentityMatrix, check the angle
// to see if it is less than okPointingAngleErrorRads.
//------------------------------------------------------------------------------
template <class P> bool
Rotation_<P>::isSameRotationToWithinAngle
   (const Rotation_<P>& R, RealP okPointingAngleErrorRads ) const {
    // The absolute minimum pointing error is 0 if "this" and R are identical.
    // The absolute maximum pointing error should be Pi (to machine precision).
    assert( 0 <= okPointingAngleErrorRads && okPointingAngleErrorRads <= Pi);
    const Rotation_<P> closeToIdentityMatrix = ~(*this) * R;
    const Vec4P angleAxisEquivalent = 
        closeToIdentityMatrix.convertRotationToAngleAxis();
    const RealP pointingError = std::abs( angleAxisEquivalent[0] );
    return pointingError <= okPointingAngleErrorRads;
}


//------------------------------------------------------------------------------
// This method is a poor man's orthogonalization from the supplied matrix to 
// make a legitimate rotation. This is done by conversion to quaternions and 
// back to Rotation and may not produce the closest rotation.
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setRotationFromApproximateMat33( const Mat33P& m ) {
    // First, create a Rotation from the given Mat33P
    const Rotation_<P> approximateRotation(m, true);
    const Quaternion_<P> q = approximateRotation.convertRotationToQuaternion();
    this->setRotationFromQuaternion( q );
    return *this;
}


//------------------------------------------------------------------------------
// Note: It may be slightly more efficient to set this matrix directly rather 
// than via the quaternion.
//------------------------------------------------------------------------------
template <class P> Rotation_<P>&
Rotation_<P>::setRotationFromAngleAboutUnitVector
  ( RealP angleInRad, const UnitVec3P& unitVector ) 
{
    QuaternionP q;
    q.setQuaternionFromAngleAxis( angleInRad, unitVector );
    return setRotationFromQuaternion( q );
}

//------------------------------------------------------------------------------
// Use sneaky tricks from Featherstone to rotate a symmetric dyadic
// matrix. Consider the current Rotation matrix to be R_AB. We want
// to return S_AA=R_AB*S_BB*R_BA. Would be 90 flops for 3x3s, 75
// since we only need six elements in final result. Here we'll get
// it done in 57 flops.
// Consider S=[ a d e ]
//            [ d b f ]
//            [ e f c ]
//
// First, factor S into S=L+D+vx with v=~[-f e 0] (x means cross 
// product matrix):
//        [a-c   d   0]     [c 0 0]       [ 0  0  e]
//    L = [ d   b-c  0] D = [0 c 0]  vx = [ 0  0  f]
//        [2e   2f   0]     [0 0 c]       [-e -f  0]
// (4 flops to calculate L)
//
// A cross product matrix identity says R*vx*~R=(R*v)x, so:
//    S'=R*S*~R = R*L*~R + D + (R*v)x. 
// Let Y'=R*L, Z=Y'*~R. We only need the lower triangle of Z and a 
// 2x2 square of Y'.
//
// Don't-care's below are marked "-". Reminder: square bracket [i]
// index of a matrix means "row i", round bracket (j) means "col j".
//
//        [  -   -  0 ]
//   Y' = [ Y00 Y01 0 ]   Y = [ R[1]*L(0)  R[1]*L(1) ]  20 flops
//        [ Y10 Y11 0 ]       [ R[2]*L(0)  R[2]*L(1) ]
//
//   Z = [   Z00           -           -      ]
//       [ Y[0]*~R[0]  Y[0]*~R[1]      -      ]   15 flops (use only 2
//       [ Y[1]*~R[0]  Y[1]*~R[1]  Y[1]*~R[2] ]   elements of R's rows)
//
//   Z00 = (L00+L11)-(Z11+Z22)  3 flops ( because rotation preserves trace)
//
//        [R01*e-R00*f]            [  0       -    -  ]
//   R*v =[R11*e-R10*f]   (R*v)x = [ Rv[2]    0    -  ]
//        [R21*e-R20*f]            [-Rv[1]  Rv[0]  0  ]
// (R*v is 9 flops)
//
//        [  Z00 + c          -           -    ]
//   S' = [ Z10 + Rv[2]   Z11 + c         -    ]
//        [ Z20 - Rv[1]  Z21 + Rv[0]   Z22 + c ]
//
// which takes 6 more flops. Total 6+9Rv+18Z+20Y+4L=57.
//
// (I actually looked at the generated code in VC++ 2005 and Intel C++
//  version 11.1 and counted exactly 57 inline flops.)
//
// NOTE: there are two implementations of this routine that have
// to be kept in sync -- this one and the identical one for 
// InverseRotation right below.
//------------------------------------------------------------------------------
template <class P> SymMat<3,P>
Rotation_<P>::reexpressSymMat33(const SymMat33P& S_BB) const {
    const RealP a=S_BB(0,0), b=S_BB(1,1), c=S_BB(2,2);
    const RealP d=S_BB(1,0), e=S_BB(2,0), f=S_BB(2,1);
    const Mat33P& R   = this->asMat33();
    const Mat32P& RR  = R.template getSubMat<3,2>(0,0); //first two columns of R

    const Mat32P L( a-c ,  d,
                     d  , b-c,
                    2*e , 2*f );

    const Mat22P Y( R[1]*L(0), R[1]*L(1),
                    R[2]*L(0), R[2]*L(1) );

    const RealP Z10 = Y[0]*~RR[0], Z11 = Y[0]*~RR[1],
                Z20 = Y[1]*~RR[0], Z21 = Y[1]*~RR[1], Z22= Y[1]*~RR[2];
    const RealP Z00 = (L(0,0)+L(1,1)) - (Z11+Z22);

    const Vec3P Rv( R(0,1)*e-R(0,0)*f,
                    R(1,1)*e-R(1,0)*f,
                    R(2,1)*e-R(2,0)*f );

    return SymMat33P( Z00 + c,
                      Z10 + Rv[2], Z11 + c,
                      Z20 - Rv[1], Z21 + Rv[0], Z22 + c );
}

// See above method for details. This method is identical except that
// the layout of the matrix used to store the rotation matrix has
// changed. Note that all the indexing here is identical to the normal
// case above; but the rotation matrix elements are drawn from different
// memory locations so that the net effect is to use the transpose of
// the original rotation from which this was created.
template <class P> SymMat<3,P>
InverseRotation_<P>::reexpressSymMat33(const SymMat<3,P>& S_BB) const {
    const P a=S_BB(0,0), b=S_BB(1,1), c=S_BB(2,2);
    const P d=S_BB(1,0), e=S_BB(2,0), f=S_BB(2,1);
    // Note reversal of row and column spacing here (normal is 3,1).
    const Mat<3,3,P,1,3>& R   = this->asMat33();
    // RR is just the first two columns of R.
    const Mat<3,2,P,1,3>& RR  = R.template getSubMat<3,2>(0,0);

    const Mat32P L( a-c ,  d,
                     d  , b-c,
                    2*e , 2*f );

    const Mat22P Y( R[1]*L(0), R[1]*L(1),
                    R[2]*L(0), R[2]*L(1) );

    const P Z10 = Y[0]*~RR[0], Z11 = Y[0]*~RR[1],
            Z20 = Y[1]*~RR[0], Z21 = Y[1]*~RR[1], Z22= Y[1]*~RR[2];
    const P Z00 = (L(0,0)+L(1,1)) - (Z11+Z22);

    const Vec3P Rv( R(0,1)*e-R(0,0)*f,
                    R(1,1)*e-R(1,0)*f,
                    R(2,1)*e-R(2,0)*f );

    return SymMat<3,P>( Z00 + c,
                      Z10 + Rv[2], Z11 + c,
                      Z20 - Rv[1], Z21 + Rv[0], Z22 + c );
}

// Make sure there are instantiations for all the non-inline methods.
template class Rotation_<float>;
template class Rotation_<double>;
template class InverseRotation_<float>;
template class InverseRotation_<double>;

//------------------------------------------------------------------------------
template <class P> std::ostream&  
operator<<( std::ostream& o, const Rotation_<P>& m ) 
{ return o << m.asMat33(); }
template <class P> std::ostream&  
operator<<( std::ostream& o, const InverseRotation_<P>& m )  
{ return o << Rotation_<P>(m); }

template SimTK_SimTKCOMMON_EXPORT std::ostream& 
operator<<(std::ostream&, const Rotation_<float>&);
template SimTK_SimTKCOMMON_EXPORT std::ostream& 
operator<<(std::ostream&, const Rotation_<double>&);

template SimTK_SimTKCOMMON_EXPORT std::ostream& 
operator<<(std::ostream&, const InverseRotation_<float>&);
template SimTK_SimTKCOMMON_EXPORT std::ostream& 
operator<<(std::ostream&, const InverseRotation_<double>&);



//------------------------------------------------------------------------------
}  // End of namespace SimTK