logisdf Documentation


PLS_Toolbox Documentation: logisdf	< laplacedf	lognormdf >

logisdf

Purpose

Logistic distribution.

Synopsis

prob = logisdf(function,x,a,b)

Description

Estimates cumulative distribution function (cumulative, cdf), probability density function (density, pdf), quantile (inverse of cdf), or random numbers for a Logistic distribution.

This distribution is a common alternative to the normal distribution. It is symmetric and many times used when data represents midpoints of interval data (data collected in such a way that a range instead or an exact value is collected). The variance may be smaller, equal, or larger than the mean for this distribution.

INPUTS:

function = [ {'cumulative'} | 'density' | 'quantile' | 'random' ], defines the functionality to be used. Note that the function recognizes the first letter of each string so that the string could be: [ 'c' | 'd' | 'q' | 'r' ].

x = matrix in which the sample data is stored, in the interval (-inf,inf).

for function=quantile - matrix with values in the interval (0,1).

for function=random - vector indicating the size of the random matrix to create.

a = mean parameter (real).

b = standard deviation parameter (real and positive).

Note: If inputs (x, a, and b) are not equal in size, the function will attempt to resize all inputs to the largest input using the RESIZE function.

Note: Functions will typically allow input values outside of the acceptable range to be passed but such values will return NaN in the results.

Examples

Cumulative:

>> prob = logisdf('c',0.99,1,2)

prob =

0.4988

>> x = [0:0.1:10];

>> plot(x,logisdf('c',x,1,2),'b-',x,logisdf('c',x,3,.5),'r-')

Density:

>> prob = logisdf('d',0.99,1,2)

prob =

0.1250

>> x = [0:0.1:10];

>> plot(x,logisdf('d',x,2,1),'b-',x,logisdf('d',x,0.5,1),'r-')

Quantile:

>> prob = logisdf('q',0.99,1,2)

prob =

10.1902

Random:

>> prob = logisdf('r',[4 1],2,1)

ans =

0.4549

0.4638

0.3426

0.5011