`Multinomial`

Inherits From: `RandomVariable`

Multinomial distribution.

This Multinomial distribution is parameterized by `probs`

, a (batch of) length-`k`

`prob`

(probability) vectors (`k > 1`

) such that `tf.reduce_sum(probs, -1) = 1`

, and a `total_count`

number of trials, i.e., the number of trials per draw from the Multinomial. It is defined over a (batch of) length-`k`

vector `counts`

such that `tf.reduce_sum(counts, -1) = total_count`

. The Multinomial is identically the Binomial distribution when `k = 2`

.

The Multinomial is a distribution over `k`

-class counts, i.e., a length-`k`

vector of non-negative integer `counts = n = [n_0, ..., n_{k-1}]`

.

The probability mass function (pmf) is,

```
pmf(n; pi, N) = prod_j (pi_j)**n_j / Z
Z = (prod_j n_j!) / N!
```

where: * `probs = pi = [pi_0, ..., pi_{k-1}]`

, `pi_j > 0`

, `sum_j pi_j = 1`

, * `total_count = N`

, `N`

a positive integer, * `Z`

is the normalization constant, and, * `N!`

denotes `N`

factorial.

Distribution parameters are automatically broadcast in all functions; see examples for details.

Create a 3-class distribution, with the 3rd class is most likely to be drawn, using logits.

```
logits = [-50., -43, 0]
dist = Multinomial(total_count=4., logits=logits)
```

Create a 3-class distribution, with the 3rd class is most likely to be drawn.

```
p = [.2, .3, .5]
dist = Multinomial(total_count=4., probs=p)
```

The distribution functions can be evaluated on counts.

```
# counts same shape as p.
counts = [1., 0, 3]
dist.prob(counts) # Shape []
# p will be broadcast to [[.2, .3, .5], [.2, .3, .5]] to match counts.
counts = [[1., 2, 1], [2, 2, 0]]
dist.prob(counts) # Shape [2]
# p will be broadcast to shape [5, 7, 3] to match counts.
counts = [[...]] # Shape [5, 7, 3]
dist.prob(counts) # Shape [5, 7]
```

Create a 2-batch of 3-class distributions.

```
p = [[.1, .2, .7], [.3, .3, .4]] # Shape [2, 3]
dist = Multinomial(total_count=[4., 5], probs=p)
counts = [[2., 1, 1], [3, 1, 1]]
dist.prob(counts) # Shape [2]
```

`allow_nan_stats`

Python `bool`

describing behavior when a stat is undefined.

Stats return +/- infinity when it makes sense. E.g., the variance of a Cauchy distribution is infinity. However, sometimes the statistic is undefined, e.g., if a distribution's pdf does not achieve a maximum within the support of the distribution, the mode is undefined. If the mean is undefined, then by definition the variance is undefined. E.g. the mean for Student's T for df = 1 is undefined (no clear way to say it is either + or - infinity), so the variance = E[(X - mean)**2] is also undefined.

: Python`allow_nan_stats`

`bool`

.

`batch_shape`

Shape of a single sample from a single event index as a `TensorShape`

.

May be partially defined or unknown.

The batch dimensions are indexes into independent, non-identical parameterizations of this distribution.

:`batch_shape`

`TensorShape`

, possibly unknown.

`dtype`

The `DType`

of `Tensor`

s handled by this `Distribution`

.

`event_shape`

Shape of a single sample from a single batch as a `TensorShape`

.

May be partially defined or unknown.

:`event_shape`

`TensorShape`

, possibly unknown.

`logits`

Vector of coordinatewise logits.

`name`

Name prepended to all ops created by this `Distribution`

.

`parameters`

Dictionary of parameters used to instantiate this `Distribution`

.

`probs`

Probability of of drawing a `1`

in that coordinate.

`reparameterization_type`

Describes how samples from the distribution are reparameterized.

Currently this is one of the static instances `distributions.FULLY_REPARAMETERIZED`

or `distributions.NOT_REPARAMETERIZED`

.

An instance of `ReparameterizationType`

.

`sample_shape`

Sample shape of random variable.

`shape`

Shape of random variable.

`total_count`

Number of trials used to construct a sample.

`unique_name`

Name of random variable with its unique scoping name. Use `name`

to just get the name of the random variable.

`validate_args`

Python `bool`

indicating possibly expensive checks are enabled.

**init**

```
__init__(
*args,
**kwargs
)
```

Initialize a batch of Multinomial distributions.

: Non-negative floating point tensor with shape broadcastable to`total_count`

`[N1,..., Nm]`

with`m >= 0`

. Defines this as a batch of`N1 x ... x Nm`

different Multinomial distributions. Its components should be equal to integer values.: Floating point tensor representing the log-odds of a positive event with shape broadcastable to`logits`

`[N1,..., Nm, k], m >= 0`

, and the same dtype as`total_count`

. Defines this as a batch of`N1 x ... x Nm`

different`k`

class Multinomial distributions. Only one of`logits`

or`probs`

should be passed in.: Positive floating point tensor with shape broadcastable to`probs`

`[N1,..., Nm, k]`

`m >= 0`

and same dtype as`total_count`

. Defines this as a batch of`N1 x ... x Nm`

different`k`

class Multinomial distributions.`probs`

's components in the last portion of its shape should sum to`1`

. Only one of`logits`

or`probs`

should be passed in.: Python`validate_args`

`bool`

, default`False`

. When`True`

distribution parameters are checked for validity despite possibly degrading runtime performance. When`False`

invalid inputs may silently render incorrect outputs.: Python`allow_nan_stats`

`bool`

, default`True`

. When`True`

, statistics (e.g., mean, mode, variance) use the value "`NaN`

" to indicate the result is undefined. When`False`

, an exception is raised if one or more of the statistic's batch members are undefined.: Python`name`

`str`

name prefixed to Ops created by this class.

**abs**

`__abs__()`

**add**

`__add__(other)`

**and**

`__and__(other)`

**bool**

`__bool__()`

**div**

`__div__(other)`

**eq**

`__eq__(other)`

**floordiv**

`__floordiv__(other)`

**ge**

`__ge__(other)`

**getitem**

`__getitem__(key)`

Subset the tensor associated to the random variable, not the random variable itself.

**gt**

`__gt__(other)`

**invert**

`__invert__()`

**iter**

`__iter__()`

**le**

`__le__(other)`

**lt**

`__lt__(other)`

**mod**

`__mod__(other)`

**mul**

`__mul__(other)`

**neg**

`__neg__()`

**nonzero**

`__nonzero__()`

**or**

`__or__(other)`

**pow**

`__pow__(other)`

**radd**

`__radd__(other)`

**rand**

`__rand__(other)`

**rdiv**

`__rdiv__(other)`

**rfloordiv**

`__rfloordiv__(other)`

**rmod**

`__rmod__(other)`

**rmul**

`__rmul__(other)`

**ror**

`__ror__(other)`

**rpow**

`__rpow__(other)`

**rsub**

`__rsub__(other)`

**rtruediv**

`__rtruediv__(other)`

**rxor**

`__rxor__(other)`

**sub**

`__sub__(other)`

**truediv**

`__truediv__(other)`

**xor**

`__xor__(other)`

`batch_shape_tensor`

`batch_shape_tensor(name='batch_shape_tensor')`

Shape of a single sample from a single event index as a 1-D `Tensor`

.

The batch dimensions are indexes into independent, non-identical parameterizations of this distribution.

: name to give to the op`name`

:`batch_shape`

`Tensor`

.

`cdf`

```
cdf(
value,
name='cdf'
)
```

Cumulative distribution function.

Given random variable `X`

, the cumulative distribution function `cdf`

is:

`cdf(x) := P[X <= x]`

:`value`

`float`

or`double`

`Tensor`

.: The name to give this op.`name`

: a`cdf`

`Tensor`

of shape`sample_shape(x) + self.batch_shape`

with values of type`self.dtype`

.

`conjugate_log_prob`

`conjugate_log_prob(val=None)`

`copy`

`copy(**override_parameters_kwargs)`

Creates a deep copy of the distribution.

Note: the copy distribution may continue to depend on the original initialization arguments.

**override_parameters_kwargs: String/value dictionary of initialization arguments to override with new values.

: A new instance of`distribution`

`type(self)`

initialized from the union of self.parameters and override_parameters_kwargs, i.e.,`dict(self.parameters, **override_parameters_kwargs)`

.

`covariance`

`covariance(name='covariance')`

Covariance.

Covariance is (possibly) defined only for non-scalar-event distributions.

For example, for a length-`k`

, vector-valued distribution, it is calculated as,

`Cov[i, j] = Covariance(X_i, X_j) = E[(X_i - E[X_i]) (X_j - E[X_j])]`

where `Cov`

is a (batch of) `k x k`

matrix, `0 <= (i, j) < k`

, and `E`

denotes expectation.

Alternatively, for non-vector, multivariate distributions (e.g., matrix-valued, Wishart), `Covariance`

shall return a (batch of) matrices under some vectorization of the events, i.e.,

`Cov[i, j] = Covariance(Vec(X)_i, Vec(X)_j) = [as above]`

where `Cov`

is a (batch of) `k' x k'`

matrices, `0 <= (i, j) < k' = reduce_prod(event_shape)`

, and `Vec`

is some function mapping indices of this distribution's event dimensions to indices of a length-`k'`

vector.

: The name to give this op.`name`

: Floating-point`covariance`

`Tensor`

with shape`[B1, ..., Bn, k', k']`

where the first`n`

dimensions are batch coordinates and`k' = reduce_prod(self.event_shape)`

.

`entropy`

`entropy(name='entropy')`

Shannon entropy in nats.

`eval`

```
eval(
session=None,
feed_dict=None
)
```

In a session, computes and returns the value of this random variable.

This is not a graph construction method, it does not add ops to the graph.

This convenience method requires a session where the graph containing this variable has been launched. If no session is passed, the default session is used.

: tf.BaseSession, optional. The`session`

`tf.Session`

to use to evaluate this random variable. If none, the default session is used.: dict, optional. A dictionary that maps`feed_dict`

`tf.Tensor`

objects to feed values. See`tf.Session.run()`

for a description of the valid feed values.

```
x = Normal(0.0, 1.0)
with tf.Session() as sess:
# Usage passing the session explicitly.
print(x.eval(sess))
# Usage with the default session. The 'with' block
# above makes 'sess' the default session.
print(x.eval())
```

`event_shape_tensor`

`event_shape_tensor(name='event_shape_tensor')`

Shape of a single sample from a single batch as a 1-D int32 `Tensor`

.

: name to give to the op`name`

:`event_shape`

`Tensor`

.

`get_ancestors`

`get_ancestors(collection=None)`

Get ancestor random variables.

`get_blanket`

`get_blanket(collection=None)`

Get the random variable's Markov blanket.

`get_children`

`get_children(collection=None)`

Get child random variables.

`get_descendants`

`get_descendants(collection=None)`

Get descendant random variables.

`get_parents`

`get_parents(collection=None)`

Get parent random variables.

`get_shape`

`get_shape()`

Get shape of random variable.

`get_siblings`

`get_siblings(collection=None)`

Get sibling random variables.

`get_variables`

`get_variables(collection=None)`

Get TensorFlow variables that the random variable depends on.

`is_scalar_batch`

`is_scalar_batch(name='is_scalar_batch')`

Indicates that `batch_shape == []`

.

: The name to give this op.`name`

:`is_scalar_batch`

`bool`

scalar`Tensor`

.

`is_scalar_event`

`is_scalar_event(name='is_scalar_event')`

Indicates that `event_shape == []`

.

: The name to give this op.`name`

:`is_scalar_event`

`bool`

scalar`Tensor`

.

`log_cdf`

```
log_cdf(
value,
name='log_cdf'
)
```

Log cumulative distribution function.

Given random variable `X`

, the cumulative distribution function `cdf`

is:

`log_cdf(x) := Log[ P[X <= x] ]`

Often, a numerical approximation can be used for `log_cdf(x)`

that yields a more accurate answer than simply taking the logarithm of the `cdf`

when `x << -1`

.

:`value`

`float`

or`double`

`Tensor`

.: The name to give this op.`name`

: a`logcdf`

`Tensor`

of shape`sample_shape(x) + self.batch_shape`

with values of type`self.dtype`

.

`log_prob`

```
log_prob(
value,
name='log_prob'
)
```

Log probability density/mass function.

Additional documentation from `Multinomial`

:

For each batch of counts, `value = [n_0, ... ,n_{k-1}]`

, `P[value]`

is the probability that after sampling `self.total_count`

draws from this Multinomial distribution, the number of draws falling in class `j`

is `n_j`

. Since this definition is exchangeable; different sequences have the same counts so the probability includes a combinatorial coefficient.

Note: `value`

must be a non-negative tensor with dtype `self.dtype`

, have no fractional components, and such that `tf.reduce_sum(value, -1) = self.total_count`

. Its shape must be broadcastable with `self.probs`

and `self.total_count`

.

:`value`

`float`

or`double`

`Tensor`

.: The name to give this op.`name`

: a`log_prob`

`Tensor`

of shape`sample_shape(x) + self.batch_shape`

with values of type`self.dtype`

.

`log_survival_function`

```
log_survival_function(
value,
name='log_survival_function'
)
```

Log survival function.

Given random variable `X`

, the survival function is defined:

```
log_survival_function(x) = Log[ P[X > x] ]
= Log[ 1 - P[X <= x] ]
= Log[ 1 - cdf(x) ]
```

Typically, different numerical approximations can be used for the log survival function, which are more accurate than `1 - cdf(x)`

when `x >> 1`

.

:`value`

`float`

or`double`

`Tensor`

.: The name to give this op.`name`

`Tensor`

of shape `sample_shape(x) + self.batch_shape`

with values of type `self.dtype`

.

`mean`

`mean(name='mean')`

Mean.

`mode`

`mode(name='mode')`

Mode.

`param_shapes`

```
param_shapes(
cls,
sample_shape,
name='DistributionParamShapes'
)
```

Shapes of parameters given the desired shape of a call to `sample()`

.

This is a class method that describes what key/value arguments are required to instantiate the given `Distribution`

so that a particular shape is returned for that instance's call to `sample()`

.

Subclasses should override class method `_param_shapes`

.

:`sample_shape`

`Tensor`

or python list/tuple. Desired shape of a call to`sample()`

.: name to prepend ops with.`name`

`dict`

of parameter name to `Tensor`

shapes.

`param_static_shapes`

```
param_static_shapes(
cls,
sample_shape
)
```

param_shapes with static (i.e. `TensorShape`

) shapes.

This is a class method that describes what key/value arguments are required to instantiate the given `Distribution`

so that a particular shape is returned for that instance's call to `sample()`

. Assumes that the sample's shape is known statically.

Subclasses should override class method `_param_shapes`

to return constant-valued tensors when constant values are fed.

:`sample_shape`

`TensorShape`

or python list/tuple. Desired shape of a call to`sample()`

.

`dict`

of parameter name to `TensorShape`

.

: if`ValueError`

`sample_shape`

is a`TensorShape`

and is not fully defined.

`prob`

```
prob(
value,
name='prob'
)
```

Probability density/mass function.

Additional documentation from `Multinomial`

:

For each batch of counts, `value = [n_0, ... ,n_{k-1}]`

, `P[value]`

is the probability that after sampling `self.total_count`

draws from this Multinomial distribution, the number of draws falling in class `j`

is `n_j`

. Since this definition is exchangeable; different sequences have the same counts so the probability includes a combinatorial coefficient.

Note: `value`

must be a non-negative tensor with dtype `self.dtype`

, have no fractional components, and such that `tf.reduce_sum(value, -1) = self.total_count`

. Its shape must be broadcastable with `self.probs`

and `self.total_count`

.

:`value`

`float`

or`double`

`Tensor`

.: The name to give this op.`name`

: a`prob`

`Tensor`

of shape`sample_shape(x) + self.batch_shape`

with values of type`self.dtype`

.

`quantile`

```
quantile(
value,
name='quantile'
)
```

Quantile function. Aka "inverse cdf" or "percent point function".

Given random variable `X`

and `p in [0, 1]`

, the `quantile`

is:

`quantile(p) := x such that P[X <= x] == p`

:`value`

`float`

or`double`

`Tensor`

.: The name to give this op.`name`

: a`quantile`

`Tensor`

of shape`sample_shape(x) + self.batch_shape`

with values of type`self.dtype`

.

`sample`

```
sample(
sample_shape=(),
seed=None,
name='sample'
)
```

Generate samples of the specified shape.

Note that a call to `sample()`

without arguments will generate a single sample.

: 0D or 1D`sample_shape`

`int32`

`Tensor`

. Shape of the generated samples.: Python integer seed for RNG`seed`

: name to give to the op.`name`

: a`samples`

`Tensor`

with prepended dimensions`sample_shape`

.

`stddev`

`stddev(name='stddev')`

Standard deviation.

Standard deviation is defined as,

`stddev = E[(X - E[X])**2]**0.5`

where `X`

is the random variable associated with this distribution, `E`

denotes expectation, and `stddev.shape = batch_shape + event_shape`

.

: The name to give this op.`name`

: Floating-point`stddev`

`Tensor`

with shape identical to`batch_shape + event_shape`

, i.e., the same shape as`self.mean()`

.

`survival_function`

```
survival_function(
value,
name='survival_function'
)
```

Survival function.

Given random variable `X`

, the survival function is defined:

```
survival_function(x) = P[X > x]
= 1 - P[X <= x]
= 1 - cdf(x).
```

:`value`

`float`

or`double`

`Tensor`

.: The name to give this op.`name`

`Tensor`

of shape `sample_shape(x) + self.batch_shape`

with values of type `self.dtype`

.

`value`

`value()`

Get tensor that the random variable corresponds to.

`variance`

`variance(name='variance')`

Variance.

Variance is defined as,

`Var = E[(X - E[X])**2]`

where `X`

is the random variable associated with this distribution, `E`

denotes expectation, and `Var.shape = batch_shape + event_shape`

.

: The name to give this op.`name`

: Floating-point`variance`

`Tensor`

with shape identical to`batch_shape + event_shape`

, i.e., the same shape as`self.mean()`

.

`support`