def to_elegant(self, filepath):
"""Generate an Elegant particle file."""
from sdds import SDDS
sd = SDDS(0)
sd.mode = sd.SDDS_BINARY
sd.description[0] = ""
sd.description[1] = ""
sd.parameterName = ["Charge"]
sd.parameterData = [[self._q]]
sd.parameterDefinition = [["", "", "", "", sd.SDDS_DOUBLE, ""]]
xp = self._data[:, 1] / self._data[:, 5] # px / pz
yp = self._data[:, 3] / self._data[:, 5] # py / pz
z = self._data[:, 4] - self._data[:, 4].mean()
x = self._data[:, 0] - z * xp
y = self._data[:, 2] - z * yp
p = np.sqrt(self._data[:, 1] ** 2
+ self._data[:, 3] ** 2
+ self._data[:, 5] ** 2)
sd.columnName = ["x", "xp", "y", "yp", "p", "t"]
sd.columnData = [[x.tolist()], [xp.tolist()],
[y.tolist()], [yp.tolist()],
[p.tolist()], [self._data[:, 6].tolist()]]
sd.columnDefinition = [["", "m", "", "", sd.SDDS_DOUBLE, 0],
["x'", "", "", "", sd.SDDS_DOUBLE, 0],
["", "m", "", "", sd.SDDS_DOUBLE, 0],
["y'", "", "", "", sd.SDDS_DOUBLE, 0],
["", "m$be$nc", "", "", sd.SDDS_DOUBLE, 0],
["", "s", "", "", sd.SDDS_DOUBLE, 0]]
sd.save(filepath)
del sd
