  Mira variables are asymptotic giant branch pulsating stars with long
pulsation periods and large amplitudes in optical bands. By applying the random
forest algorithm to the I-band light curves for the Miras in the Magellanic
Clouds, we have classified these Miras into regular Miras and non-regular
Miras. Wherein non-regular Miras exhibit a long-term variation in addition to
their primary pulsation periods. Our results confirm that the period-luminosity
relation for maximum light has a smaller dispersion, but only occurs on the
regular oxygen-rich (O-rich) Miras, which we recommend to be applied in future
distance scale work. We have also collected multi-band photometry for these
Miras to perform a spectral-energy-distribution (SED) fitting with stellar and
dust components, showing that a significant fraction of dust is present around
the non-regular Miras. According to our results, we believe that the periodic
long-term variations seen in the non-regular Miras might be due to the presence
of dust.
