ufunc
numpy.ctypeslib
numpy.dual
numpy.emath
numpy.fft
numpy.linalg
numpy.matlib
numpy.polynomial.polynomial
numpy.polynomial.chebyshev
numpy.polynomial.hermite
numpy.polynomial.hermite_e
numpy.polynomial.laguerre
numpy.polynomial.legendre
numpy.random
numpy.testing
numpy.typing
numpy.distutils
Issued by polyfit when the Vandermonde matrix is rank deficient.
polyfit
For more information, a way to suppress the warning, and an example of RankWarning being issued, see polyfit.
RankWarning