Documentation/How Tos/Calc: CHISQDIST function

From OpenOffice.org Wiki

Jump to: navigation, search

This function is not yet implemented but expected for OpenOffice.org version 3.1.

CHISQDIST

Calculates values for a χ2-distribution.

Syntax

CHISQDIST(x; k; Cumulative)

x is the number, at which you will evaluate the χ2-distribution.
k sets the degrees of freedom for the χ2-distribution
Constraint: k must be a positive integer
Cumulative is a logical value.
In the case Cumulative=TRUE() the cumulative distribution function is used, in the case Cumulative=FALSE() the probability density function. This parameter is optional. It is set to TRUE() if missing.

Semantic

CHISQDIST(x;k;FALSE()) returns values of the probability density function for the χ2-distribution:

= \begin{cases} 0, & \textrm{if}\; x \le 0 \\ \displaystyle \frac {x^{\frac k 2 -1}\,\mathrm e^{- \frac x 2}} {2^{\frac k 2}\,\Gamma(\frac k 2) }, & \textrm{if}\; x > 0 \end{cases}

CHISQDIST(x;k;TRUE()) returns the left tail probability for the χ2-distribution:

= \begin{cases} 0, & \textrm{if}\; x \le 0 \\ \displaystyle \int_0^x \frac {t^{\frac k 2 -1}\,\mathrm e^{- \frac t 2}} {2^{\frac k 2}\,\Gamma(\frac k 2) }\,\mathrm d t, & \textrm{if}\; x > 0 \end{cases}

Example

CHISQDIST(2.3;15;FALSE())
returns approximately 0,000209862

CHISQDIST(2.3;2;FALSE())

returns approximately 0,158318385
Graphs of Chi-distribution density functions
CHISQDIST(1.5;2;TRUE())
returns approximately 0,5276334

other valid call: CHISQDIST(1.5;2)

Chi-distribution cumulative functions
CHISQDIST(18;15;TRUE())
returns approximately 0,73733444
Area under density function

Chi-distribution with marked point

Remarks

If you need CHISQDIST(x;k;TRUE()) with a non integer parameter k, then use GAMMADIST(x;k/2;2) instead.

For to get the right tail for large values x, do not calculate 1 − CHISQDIST. It is less accurate in those cases than using CHIDIST. CHISQDIST(x;k;TRUE()) + CHIDIST(x;k) = 1.

In the density case the internal calculation uses logarithmic- and exponential function, if x >1425 or x · k > 1391000. The results are less accurate in those cases.

Issues

This function is not available in version 3.0 and earlier.


See Also

Retrieved from "http://wiki.services.openoffice.org/wiki/Documentation/How_Tos/Calc:_CHISQDIST_function"
Personal tools
Create a book