[build-system]
requires = ["setuptools", "wheel", "Cython", "numpy", "scipy"]

[build-system]
requires = [
    "setuptools",
    "wheel",
    "cython>=0.29.20",
    "numpy>=1.16.6,<1.20",
    "scipy>=1.0",
]

Fix build version of numpy to <1.20
Fix build version of numpy to <1.20

Numpy 1.20 changed the C-API size of ndarray to be larger.  C code
compiled against the 1.20 C-API will not handle pre-1.20 code correctly,
while code compiled from 1.16.6 <= x < 1.20 will (the lower limit is
required for some variable structures).

QuTiP will be compatible with Numpy >= 1.20, but the build system will
need the lower version if the binaries are distributed from one build
system to a different runner.
