scipy.special.chndtridf#

scipy.special.chndtridf(x, p, nc, out=None) = <wrapped_ufunc 'chndtridf'>#

Inverse to chndtr vs df.

Calculated using a search to find a value for df that produces the desired value of p.

Parameters:

xarray_like: Upper bound of the integral; must satisfy x >= 0
parray_like: Probability; must satisfy 0 <= p < 1
ncarray_like: Non-centrality parameter; must satisfy nc >= 0
outndarray, optional: Optional output array for the function results

Returns:

dfscalar or ndarray: Degrees of freedom

See also

chndtr: Noncentral chi-squared distribution CDF
chndtrix: inverse of chndtr with respect to x
chndtrinc: inverse of chndtr with respect to nc
scipy.stats.ncx2: Non-central chi-squared distribution

Notes

The noncentral chi squared distribution is also available in scipy.stats.ncx2.

This function wraps routines from the Boost Math C++ library [1].

Array API Standard Support

chndtridf has support for Python Array API Standard compatible backends in addition to NumPy. The following combinations of backend and device (or other capability) are supported.

Library	CPU	GPU
NumPy	✅	n/a
CuPy	n/a	⛔
PyTorch	✅	⛔
JAX	✅	⛔
Dask	✅	n/a

For the NumPy backend, this function supports all NumPy ufunc keyword arguments. Other backends may support out, but typically none of the other ufunc kwargs. out is typically supported for CuPy and PyTorch, but not currently in cases where SciPy relies on a generic Array API implementation or, for PyTorch on CPU, falls back to the NumPy backend. out is never supported for JAX because JAX arrays are immutable. chndtridf does not currently support out for the PyTorch backend.

See Support for the array API standard for more information.

References

[1]

The Boost Developers. “Boost C++ Libraries”. https://www.boost.org/.

Examples

>>> from scipy.special import chndtridf, chndtr

Compute the noncentral chi squared distribution CDF at one point.

>>> x, df, nc = 3, 5, 10
>>> p = chndtr(x, df, nc)

chndtridf is the inverse of chndtr with respect to df:

>>> chndtridf(x, p, nc)
5.0