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IGPDFName:
with and denoting the shape parameters. The inverse Gaussian distribution has mean and standard deviation . The inverse Gaussian distribution can be generalized with location and scale parameters in the usual way.
<SUBSET/EXCEPT/FOR qualification> where <x> is a variable or a parameter; <gamma> is number or parameter that specifies the first shape parameter; <mu> is number or parameter that specifies the second shape parameter; <loc> is number or parameter that specifies the location parameter; <scale> is number or parameter that specifies the scale parameter; <y> is a variable or a parameter (depending on what <x> is) where the computed inverse Gaussian pdf value is stored; and where the <SUBSET/EXCEPT/FOR qualification> is optional. Note that the location and scale parameters are optional.
LET A = IGPDF(A1,2,1) LET X2 = IGPDF(X1,2,3) PLOT IGPDF(X,2,1.5) FOR X = 0.1 0.1 5
LET MU = <value> LET Y = INVERSE GAUSSIAN RANDOM NUMBERS FOR I = 1 1 N INVERSE GAUSSIAN PROBABILITY PLOT Y INVERSE GAUSSIAN KOLMOGOROV-SMIRNOV GOODNESS OF FIT Y INVERSE GAUSSIAN CHI-SQUARE FIT Y The following commands can be used to generate estimates for the shape parameters of the inverse Gaussian distribution:
LET GAMMA2 = <valuee> LET MU1 = <value> LET MU2 = <value> INVERSE GAUSSIAN PPCC PLOT Y INVERSE GAUSSIAN KS PLOT Y The default values for GAMMA1 and GAMMA2 are 0.5 and 25. The default values for MU1 and MU2 are 0.5 and 25. Maximum likelihood estimates can be obtained by entering the command
The maximum likelihood estimates are
with and n denoting the sample mean and sample size, respectively.
"Statistical Distributions", Third Edition, Evans, Hastings, and Peacock, Wiley, 2000, pp. 114-116.
2003/12: Modified to treat mu as a shape parameter instead of a location parameter Y1LABEL Probability X1LABEL X LABEL CASE ASIS X1LABEL DISPLACEMENT 12 Y1LABEL DISPLACEMENT 12 MULTIPLOT SCALE FACTOR 2 MULTIPLOT 2 2 MULTIPLOT CORNER COORDINATES 0 0 100 100 YLIMITS 0 1.5 TITLE GAMMA = 2, MU = 1 PLOT IGPDF(X,2,1) FOR X = 0.01 0.01 5 TITLE GAMMA = 5, MU = 1 PLOT IGPDF(X,5,1) FOR X = 0.01 0.01 5 TITLE GAMMA = 2, MU = 2 PLOT IGPDF(X,2,2) FOR X = 0.01 0.01 5 TITLE GAMMA = 5, MU = 2 PLOT IGPDF(X,5,2) FOR X = 0.01 0.01 5 END OF MULTIPLOT JUSTIFICATION CENTER MOVE 50 97 CASE ASIS TEXT Inverse Gaussian PDF
Date created: 7/7/2004 |