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Справка Scilab >> Statistics > cdf > cdfchi

# cdfchi

cumulative distribution function chi-square distribution

### Calling Sequence

```[P,Q]=cdfchi("PQ",X,Df)
[X]=cdfchi("X",Df,P,Q);
[Df]=cdfchi("Df",P,Q,X)```

### Arguments

P,Q,Xn,Df

four real vectors of the same size.

P,Q (Q=1-P)

The integral from 0 to X of the chi-square distribution. Input range: [0, 1].

X

Upper limit of integration of the non-central chi-square distribution. Input range: [0, +infinity). Search range: [0,1E300]

Df

Degrees of freedom of the chi-square distribution. Input range: (0, +infinity). Search range: [ 1E-300, 1E300]

### Description

Calculates any one parameter of the chi-square distribution given values for the others.

Formula 26.4.19 of Abramowitz and Stegun, Handbook of Mathematical Functions (1966) is used to reduce the chi-square distribution to the incomplete distribution.

Computation of other parameters involve a search for a value that produces the desired value of P. The search relies on the monotonicity of P with the other parameter.

In certain cases, the degrees of freedom are not integers. Scilab then issues a warning.

From DCDFLIB: Library of Fortran Routines for Cumulative Distribution Functions, Inverses, and Other Parameters (February, 1994) Barry W. Brown, James Lovato and Kathy Russell. The University of Texas.

### Examples

In the following example, we compute the probability of the event `x=0.1` for the chi-square distribution function with `Df=2`.

```Df = 2;
x = 0.1;
// Expected : P = 0.0487706 and Q = 1-P
[P, Q] = cdfchi("PQ", x, Df)```

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