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#include "primitives/Bend.hpp"
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namespace oopse {
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/**@todo still a lot left to improve*/
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void Bend::calcForce() {
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Vector3d pos1 = atom1_->getPos();
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Vector3d pos2 = atom2_->getPos();
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Vector3d pos3 = atom3_->getPos();
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Vector3d r12 = pos1 - pos2;
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double d12 = r12.length();
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double d12inv = 1. 0 / d12;
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Vector3d r32 = pos3 - pos2;
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double d32 = r32.length();
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double d32inv = 1. 0 / d32;
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double cosTheta = (r12*r32)/(d12*d32);
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//check roundoff
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if (cosTheta > 1.0) {
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cosTheta = 1.0;
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} else if (cosTheta < -1.0) {
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cosTheta = -1.0;
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}
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double theta = acos(cosTheta);
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double firstDerivative;
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bendType_->calcForce(theta, firstDerivative, potential_);
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double sinTheta = sqrt(1.0 - cosTheta*cosTheta);
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if(fabs(sinTheta) < 1.0E-12 ) {
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sinTheta = 1.0E-12;
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}
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double commonFactor1 = - firstDerivative / sinTheta * d12inv;
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double commonFactor2 = - firstDerivative / sinTheta * d32inv;
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Vector3d force1 = commonFactor1*(r12*(d12inv*cosTheta) - r32*d32inv);
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Vector3d force3 = commonFactor2*(r32*(d32inv*cosTheta) - r12*d12inv);
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//total force in current bend is zero
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Vector3d force2 = force1 + force3;
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force2 *= -1.0;
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atom1_->addFrc( force1);
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atom2_->addFrc(force2);
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atom3_->addFrc(force3);
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}
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double k = value->k * scale;
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double theta0 = value->theta0;
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double diff = theta - theta0;
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double energy = k *diff*diff;
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double firstDerivative = 2.0 * k * diff;
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}//end namespace oopse
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