GammaDist | R Documentation |
Density, distribution function, quantile function and random generation for the Gamma distribution with parameters mean
and sd
. These are wrappers for stats::dgamma
, etc. getGammaPar
returns the shape and rate parameters.
dgamma2(x, mean, sd) pgamma2(q, mean, sd, lower.tail=TRUE, log.p=FALSE) qgamma2(p, mean, sd, lower.tail=TRUE, log.p=FALSE) rgamma2(n, mean, sd) getGammaPar(mean, sd)
x |
vector of parameter values |
q |
vector of quantiles |
p |
vector of probabilities |
n |
number of random draws required. |
mean |
mean of the gamma distribution |
sd |
standard deviation of the gamma distribution |
lower.tail |
logical; if TRUE (default), cumulative probabilities up to x, otherwise, above x. |
log.p |
logical; if TRUE, probabilities p are given as log(p). |
dgamma2
gives the density, pgamma2
gives the distribution function, qgamma2
gives the quantile function, and rgamma2
generates random deviates.
getGammaPar
returns a 2-column matrix with the shape and rate parameters corresponding to mean
and sd
.
Mike Meredith
See the stats functions dgamma
, pgamma
, qgamma
, rgamma
.
# Plot some curves with dgamma2 xx <- seq(0, 20, length.out=101) plot(xx, dgamma2(xx, 5, 1), xlab="x", ylab="Probability density", main="Gamma curves with mean = 5", type='l', lwd=2) lines(xx, dgamma2(xx, 5, 2), col='darkgreen', lwd=2) lines(xx, dgamma2(xx, 5, 4), col='red', lwd=2) lines(xx, dgamma2(xx, 5, 8), col='blue', lwd=2) abline(v=5, lty=3, lwd=2) legend('topright', paste("sd =", c(1,2,4,8)), lwd=2, col=c('black', 'darkgreen', 'red', 'blue'), bty='n') # Cumulative plots with pgamma2 plot(xx, pgamma2(xx, 5, 1), xlab="x", ylab="Cumulative probability", main="Gamma curves with mean = 5", type='l', lwd=2) lines(xx, pgamma2(xx, 5, 2), col='darkgreen', lwd=2) lines(xx, pgamma2(xx, 5, 4), col='red', lwd=2) lines(xx, pgamma2(xx, 5, 8), col='blue', lwd=2) abline(v=5, lty=3, lwd=2) legend('bottomright', paste("sd =", c(1,2,4,8)), lwd=2, col=c('black', 'darkgreen', 'red', 'blue'), bty='n') # Generate random draws and plot a histogram rnd <- rgamma2(1e5, 5, 2) hist(rnd, freq=FALSE) # Add the curve: lines(xx, dgamma2(xx, 5, 2), col='darkgreen', lwd=2) # Get shape and rate parameters for mean = 5 and sd = c(1,2,4,8) getGammaPar(mean = 5, sd = c(1,2,4,8))
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