WBLDF

This function evaluates the Weibull cumulative distribution function.

Function Return Value

WBLDF — Function value, the probability that a Weibull random variable takes a value less than or equal to X. (Output)

Required Arguments

X — Argument for which the Weibull cumulative distribution function is to be evaluated. (Input)

A — Scale parameter. (Input)

B — Shape parameter. (Input)

FORTRAN 90 Interface

Generic: WBLDF (X, A, B)

Specific: The specific interface names are S_WBLDF and D_WBLDF.

FORTRAN 77 Interface

Single: WBLDF (X, A, B)

Double: The double precision name is DWBLDF.

Description

The function WBLDF evaluates the Weibull cumulative distribution function with scale parameter A and shape parameter B, defined

 

To deal with potential loss of precision for small values of , the difference expression for
p is re-written as

 

and the right factor is accurately evaluated using EXPRL.

Example

In this example, we evaluate the Weibull cumulative distribution function at X = 1.5, A = 1.0, B = 2.0.

 

USE UMACH_INT

USE WBLDF_INT

IMPLICIT NONE

INTEGER NOUT

REAL X, A, B, PR

CALL UMACH(2, NOUT)

X = 1.5

A = 1.0

B = 2.0

PR = WBLDF(X, A, B)

WRITE (NOUT, 99999) X, A, B, PR

99999 FORMAT (' WBLDF(', F4.2, ', ', F4.2, ', ', F4.2, ') = ', F6.4)

END

Output

 

WBLDF(1.50, 1.00, 2.00) = 0.8946