double precision function kget_track_err_phi(ktrk)
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*  Returns the phi error of a track to the caller.
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*  Input Parameters:
*  ktrk         integer variable
*               Track number
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*  Output Parameters:
*  None
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*  Return value:
*  Error on mass
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*  Other routines:
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*  Notes:
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*   The equation for phi can be written as
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*         cot(phi) = Px / Py
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*   so    dphi = (-Py*dPx + Px*dPy) / (Px**2 + Py**2)
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*   The covariance matrix of the momentum is then
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*       sig**2 = A*Vx0*A(t)
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*    where A = (-Py, Px, 0, 0) / (Px**2 + Py**2)
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*  Author:   Paul Avery      Created:  Tue Aug 26 19:35:08 EDT 1997
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*  Major revisions:
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