ZeroModifiedGeometric | R Documentation |
Density function, distribution function, quantile function and random
generation for the Zero-Modified Geometric distribution with
parameter prob
and arbitrary probability at zero p0
.
dzmgeom(x, prob, p0, log = FALSE)
pzmgeom(q, prob, p0, lower.tail = TRUE, log.p = FALSE)
qzmgeom(p, prob, p0, lower.tail = TRUE, log.p = FALSE)
rzmgeom(n, prob, p0)
x |
vector of (strictly positive integer) quantiles. |
q |
vector of quantiles. |
p |
vector of probabilities. |
n |
number of observations. If |
prob |
parameter. |
p0 |
probability mass at zero. |
log, log.p |
logical; if |
lower.tail |
logical; if |
The zero-modified geometric distribution with prob
= p
and p0
= p_0
is a discrete mixture between a
degenerate distribution at zero and a (standard) geometric. The
probability mass function is p(0) = p_0
and
%
p(x) = \frac{(1-p_0)}{(1-p)} f(x)
for x = 1, 2, \ldots
, 0 < p < 1
and 0 \le
p_0 \le 1
, where f(x)
is the probability mass
function of the geometric.
The cumulative distribution function is
P(x) = p_0 + (1 - p_0) \left(\frac{F(x) - F(0)}{1 - F(0)}\right)
The mean is (1-p_0) \mu
and the variance is
(1-p_0) \sigma^2 + p_0(1-p_0) \mu^2
,
where \mu
and \sigma^2
are the mean and variance of
the zero-truncated geometric.
In the terminology of Klugman et al. (2012), the zero-modified
geometric is a member of the (a, b, 1)
class of
distributions with a = 1-p
and b = 0
.
The special case p0 == 0
is the zero-truncated geometric.
If an element of x
is not integer, the result of
dzmgeom
is zero, with a warning.
The quantile is defined as the smallest value x
such that
P(x) \ge p
, where P
is the distribution function.
dzmgeom
gives the (log) probability mass function,
pzmgeom
gives the (log) distribution function,
qzmgeom
gives the quantile function, and
rzmgeom
generates random deviates.
Invalid prob
or p0
will result in return value
NaN
, with a warning.
The length of the result is determined by n
for
rzmgeom
, and is the maximum of the lengths of the
numerical arguments for the other functions.
Functions {d,p,q}zmgeom
use {d,p,q}geom
for all but
the trivial input values and p(0)
.
Vincent Goulet vincent.goulet@act.ulaval.ca
Klugman, S. A., Panjer, H. H. and Willmot, G. E. (2012), Loss Models, From Data to Decisions, Fourth Edition, Wiley.
dgeom
for the geometric distribution.
dztgeom
for the zero-truncated geometric distribution.
dzmnbinom
for the zero-modified negative binomial, of
which the zero-modified geometric is a special case.
p <- 1/(1 + 0.5)
dzmgeom(1:5, prob = p, p0 = 0.6)
(1-0.6) * dgeom(1:5, p)/pgeom(0, p, lower = FALSE) # same
## simple relation between survival functions
pzmgeom(0:5, p, p0 = 0.2, lower = FALSE)
(1-0.2) * pgeom(0:5, p, lower = FALSE)/pgeom(0, p, lower = FALSE) # same
qzmgeom(pzmgeom(0:10, 0.3, p0 = 0.6), 0.3, p0 = 0.6)
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