BmnMeasureLin4.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
 
    BmnMeasureLin4 class header-only implementation
    Reduced measurement model: 3 shifts + rotation about Z axis only
    (phi and theta, the rotations about X and Y, are excluded).
*/
 
#ifndef BMNMEASURELIN4_H
#define BMNMEASURELIN4_H
 
#include "BmnMeasureModel.h"
 
/*
 * Same linearized transformation as BmnMeasureLin6 with phi = theta = 0.
 *
 * IMPORTANT: The formulae below are just reduced versions of full
 *            BmnMeasureLin6 model -- they was not checked separately.
 *
 *      R_z =  | 1    -psi  0 |
 *             | psi   1    0 |
 *             | 0     0    1 |
 *
 *      x_m = alpha_x + beta_x * z0 + dx - dz * beta_x_bar - psi * y_bar
 *      y_m = alpha_y + beta_y * z0 + dy - dz * beta_y_bar + psi * x_bar
 *
 * IMPORTANT: The phi and theta 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 BmnMeasureLin4 : 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 - gl(iPsi) * (lc(iY0) + lc(iY1) * z0);
    }
 
    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 + gl(iPsi) * (lc(iX0) + lc(iX1) * z0);
    }
 
    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
            -(lc(iY0) + lc(iY1) * z0)   // d/dpsi = -y_bar
        };
    }
 
    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
            lc(iX0) + lc(iX1) * z0   // d/dpsi = x_bar
        };
    }
 
    inline Bool_t AlignHit(FairHit& hit, const SVectGL& a) const noexcept override
    {
        SMatr3x3 rot{RM::SMatrixIdentity()};
        rot(1, 0) = a(iPsi);
        rot(0, 1) = -a(iPsi);
 
        Int_t ifail;
        SVect3 hitAligned{rot.InverseFast(ifail) * SVect3(hit.GetX() - a(idX), hit.GetY() - a(idY), -a(idZ))};
        if (ifail)
            return kFALSE;
 
        hit.SetXYZ(hitAligned(iX), hitAligned(iY), hitAligned(iZ) + hit.GetZ());
        return kTRUE;
    }
 
    inline void AlignHitApproximately(SVect3& hit, const SVectGL& a) const noexcept override
    {
        // First order approximate correction (Z rotation only)
        const Double_t x_m{hit(iX)}, y_m{hit(iY)};
        hit(iX) -= a(iX) - a(iPsi) * y_m;
        hit(iY) -= a(iY) + a(iPsi) * x_m;
        hit(iZ) -= a(iZ);
    }
};
 
#endif   // BMNMEASURELIN4_H