Difference between revisions of "User:Regina"

Revision as of 17:33, 6 October 2008

native language

German

active in project

de, qa. sc

OOo user name

regina

special interest

www.ooowiki.de

Anleitung

Sandbox

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:

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

Example

CHSQDIST(2.7;3;FALSE())

returns approximately 0.1699395239

CHSQDIST(2.7;3;TRUE())

returns approximately 0.5597727056

Remarks

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

In the density case the internal calculation uses logarithmic- and exponential function, if x >1425 or x · k > 1391000. Therefore it is less accurate then than in other cases.

See also:

CHISQINV, LEGACY.CHIDIST, LEGACY.CHIINV, CHITEST

Statistical functions

Functions listed alphabetically, Functions listed by category

Issues:

This function is expected for OOo3.1

CHISQINV

Calculates the inverse of the CHISQDIST function.

Syntax

CHISQINV(p; k)

k is the degrees of freedom for the χ²-distribution.

Constraint: k must be a positive integer

p is the given probability

Constraint: 0 ≤ p < 1

Semantic

CHISQINV(p; k) returns the value x, such that CHISQDIST(x; k;TRUE()) = p.

Example

CHISQINV(0.5; 9)

returns approximately 8.342832692

.

Remarks

If you need CHISQINV(p;k) for a non interger parameter k, then use GAMMAINV(p;k/2;2) instead.

See also:

CHISQDIST CHIDIST CHIINV

Statistical functions

Functions listed alphabetically, Functions listed by category

Issues:

• This function is expected for OOo3.1

GAMMA

Returns the values of the Gamma function.

Syntax

GAMMA(x)

x is a number.

Constraint: If x is an integer, then x must be positive.

Semantic

GAMMA(x) calculates

.

Example

GAMMA(4) = 6.0 exact

GAMMA(34.56) ≈ 6.2336323276E+037

GAMMA(−4) not defined

Remarks

For x < 0.5 Eulers reflection formula is used.

The Gamma function has poles for negative integers and for zero. Near the poles the values are less accurate.

If x is a positive integer, then

But be aware, that OpenOffice.org has only a precision of 15 digits, therefore the results for x > 21 are rounded.

See also:

GAMMALN, GAMMADIST, GAMMAINV, FACT

Mathematical functions

Statistical functions

Functions listed alphabetically, Functions listed by category

Issues:

This function is expected for OOo3.1.

Accuracy

Precision in Calc

Calc uses for its calculation floating point numbers in double precision as defined in IEEE 754 standard. You get the best representation in a spreadsheet cell using the scientific format with format code 0.00000000000000E+000. But because a binary format is used internally, the numbers in calculation might differ slightly from the shown decimal values. Only integers in the range can be represented exactly in the internal format.

Although you can force Calc to show 15 decimal digits, these might not be all accurate. This article lists some of the problems.

Cancellation

If you subtract two non integer numbers, which have nearly the same value, the result has less significant digits then the initial values.

Cell A4 shows the correct result of , calculated with a computer algebra system with high precision.

Converting Inaccuracy

Most non integer numbers have infinite decimal places in binary format, which has to be rounded somewhere. Calculating with this rounded values and converting back to decimal format gives different values then calculating manually in decimal format.

No Symbolic π

From mathematics you know sin(π)= 0 and you know that tan(π/2) is undefined. But you cannot get this in Calc, because the value π is always treated as rounded floating point number. It makes no difference using PI() or RADIANDS(180). Calc cannot evaluate π symbolically as computer algebra systems do. That is no special limitation of Calc, but other often used spreadsheet applications work only numerically too.