BmnMeasureLin3.h

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/*
    BM@N alignment routine
    BM@N experiment at NICA complex, JINR, 2025
 
    Department: Math & Soft Group of HEP lab
    Author:     Igor Polev, polev@jinr.int
 
    BmnMeasureLin3 class header-only implementation
    Reduced measurement model: 3 shifts only, no rotations at all
    (phi, theta and psi are all excluded).
*/
 
#ifndef BMNMEASURELIN3_H
#define BMNMEASURELIN3_H
 
#include "BmnMeasureModel.h"
 
/*
 * Same linearized transformation as BmnMeasureLin6 with phi = theta = psi = 0,
 * so the rotation matrix is the identity and only the shift survives.
 *
 * IMPORTANT: The formulae below are just reduced versions of full
 *            BmnMeasureLin6 model -- they was not checked separately.
 *
 *      x_m = alpha_x + beta_x * z0 + dx - dz * beta_x_bar
 *      y_m = alpha_y + beta_y * z0 + dy - dz * beta_y_bar
 *
 * IMPORTANT: The phi, theta and psi slots of the parameter vector stay
 *            in place but carry no effect (SVectGL is fixed size 6).
 *            Do not forget to add the corresponding constraints!
 */
 
class BmnMeasureLin3 : public BmnMeasureModel
{
  public:
    const char* Description() const noexcept override;   // out of line: anchors the vtable
 
    inline Double_t X(Double_t z0, const SVectGL& gl, const SVectLC& lc) const noexcept override
    {
        const Double_t beta_x{lc(iX1)};
        return lc(iX0) + beta_x * z0 + gl(idX) - gl(idZ) * beta_x;
    }
 
    inline Double_t Y(Double_t z0, const SVectGL& gl, const SVectLC& lc) const noexcept override
    {
        const Double_t beta_y{lc(iY1)};
        return lc(iY0) + beta_y * z0 + gl(idY) - gl(idZ) * beta_y;
    }
 
    inline SVectGL dXdA(Double_t /*z0*/, const SVectLC& lc) const noexcept override
    {
        return SVectGL{
            1.0,      0.0,
            -lc(iX1),   // d/ddZ = -beta_x
            0.0,        // d/dphi   excluded
            0.0,        // d/dtheta excluded
            0.0         // d/dpsi   excluded
        };
    }
 
    inline SVectGL dYdA(Double_t /*z0*/, const SVectLC& lc) const noexcept override
    {
        return SVectGL{
            0.0,      1.0,
            -lc(iY1),   // d/ddZ = -beta_y
            0.0,        // d/dphi   excluded
            0.0,        // d/dtheta excluded
            0.0         // d/dpsi   excluded
        };
    }
 
    inline Bool_t AlignHit(FairHit& hit, const SVectGL& a) const noexcept override
    {
        // no rotation to undo: the exact correction is the shift itself
        hit.SetXYZ(hit.GetX() - a(idX), hit.GetY() - a(idY), hit.GetZ() - a(idZ));
        return kTRUE;
    }
 
    inline void AlignHitApproximately(SVect3& hit, const SVectGL& a) const noexcept override
    {
        hit(iX) -= a(idX);
        hit(iY) -= a(idY);
        hit(iZ) -= a(idZ);
    }
};
 
#endif   // BMNMEASURELIN3_H