Cumulative distribution function for the Inverse-gamma distribution

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gnuplot source under GPL:

dinvgamma(x,a,b) = exp(a*log(b) - lgamma(a) - (a+1)*log(x) - b*1.0/x)
pinvgamma(x,a,b) = 1 - igamma(a, b*1.0/x)

set xtics 0,0.5
set ytics 0,0.5
set samples 1001
set terminal postscript enhanced color solid lw 2 "Times-Roman" 27
set output

plot [0:3] \
    pinvgamma(x,1,1)  title "{/Symbol a} = 1, {/Symbol b} = 1", \
    pinvgamma(x,2,1)  title "{/Symbol a} = 2, {/Symbol b} = 1", \
    pinvgamma(x,3,1)  title "{/Symbol a} = 3, {/Symbol b} = 1", \
    pinvgamma(x,3,.5) title "{/Symbol a} = 3, {/Symbol b} = 0.5"

 

This plot was created with Gnuplot.

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