Bug Report: Incorrect Calculation of Lower Triangularity in triangularityLower()

[renyihui18]

Hi,

I’ve found a bug in the triangularityLower() method when installing FreeGS via pip install --user freegs.

The triangularityLower() method in Equilibrium class currently calculates the upper triangularity instead of the lower triangularity due to using the same code with triangularityUpper().

This is the code from the installed freegs package :

    def triangularityLower(self, npoints=360):
        """Calculates plasma upper triangularity, delta_u.
        P4 is the point at the lower extent of the plasma.

        tri_l = (R0 - R(P4))/a
        """

        # Get points along the LCFS
        separatrix = self.separatrix(npoints=npoints)  # Array [:,2]
        Rlcfs = np.array([i[0] for i in separatrix])
        Zlcfs = np.array([i[1] for i in separatrix])

        ind_P2 = np.argmax(Zlcfs)

        R_P2 = Rlcfs[ind_P2]

        R0 = self.Rgeometric(npoints=npoints)
        a = self.minorRadius(npoints=npoints)

        return (R0 - R_P2) / a

This is the correct implementation (the code on GitHub is correct):

def triangularityLower(self, npoints=360):
        """Calculates plasma lower triangularity, delta_u.
        P4 is the point at the lower extent of the plasma.

        tri_l = (R0 - R(P4))/a
        """

        # Get points along the LCFS
        separatrix = self.separatrix(npoints=npoints)  # Array [:,2]
        Rlcfs = np.array([i[0] for i in separatrix])
        Zlcfs = np.array([i[1] for i in separatrix])

        ind_P4 = np.argmin(Zlcfs)

        R_P4 = Rlcfs[ind_P4]

        R0 = self.Rgeometric(npoints=npoints)
        a = self.minorRadius(npoints=npoints)

        return (R0 - R_P4) / a

[bendudson]

Thanks @renyihui18 for the bug report! This was fixed in master in April (PR #127), but it looks like we need to update the version on PyPI. For now I recommend installing the github version.