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change rate parameter in Poisson to Float32 #147

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Merged
marcelluethi merged 2 commits into from
Aug 18, 2026
Merged

change rate parameter in Poisson to Float32 #147

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2863ab8
change rate parameter in Poisson to Float32
marcelluethi Aug 16, 2026
55273e4
add separate vtype for rate
marcelluethi Aug 16, 2026
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20 changes: 15 additions & 5 deletions core/src/main/scala/dimwit/stats/IndependentDistributions.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -216,12 +216,22 @@ class Exponential[T <: Tuple: Labels, V: IsFloating](val rate: Tensor[T, V]) ext
)
stndExp / rate

class Poisson[T <: Tuple: Labels, V: IsInteger](val rate: Tensor[T, V]) extends IndependentDistribution[T, V]:
class Poisson[T <: Tuple: Labels, VSample: IsInteger, VRate: IsFloating](val rate: Tensor[T, VRate]) extends IndependentDistribution[T, VSample]:

override def elementWiseLogProb(x: Tensor[T, V]): Tensor[T, LogProb] =
override def elementWiseLogProb(x: Tensor[T, VSample]): Tensor[T, LogProb] =
liftPyTensor(jstats.poisson.logpmf(x.jaxValue, mu = rate.jaxValue))

override def sample(k: Random.Key): Tensor[T, V] =
liftPyTensor(
Jax.jrandom.poisson(k.jaxKey, lam = rate.jaxValue, shape = rate.shape.dimensions.toPythonProxy)
override def sample(k: Random.Key): Tensor[T, VSample] =
liftPyTensor(rate.shape, VType[VSample])(
Jax.jrandom.poisson(k.jaxKey, lam = rate.jaxValue, shape = rate.shape.dimensions.toPythonProxy, dtype = VType[VSample].dtype.jaxType)
)

object Poisson:

/** Create a Poisson distribution from a rate tensor, sampling as Int32 counts */
def apply[T <: Tuple: Labels, VRate: IsFloating](rate: Tensor[T, VRate]): Poisson[T, Int32, VRate] =
new Poisson[T, Int32, VRate](rate)

/** Create a Poisson distribution from a rate tensor, sampling counts of the given integer type */
def apply[T <: Tuple: Labels, VSample: IsInteger, VRate: IsFloating](rate: Tensor[T, VRate], vtype: VType[VSample]): Poisson[T, VSample, VRate] =
new Poisson[T, VSample, VRate](rate)
4 changes: 2 additions & 2 deletions core/src/test/scala/dimwit/stats/DistributionSuite.scala
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Expand Up @@ -401,7 +401,7 @@ class DistributionSuite extends DimwitTest:

describe("Poisson"):
it("logProbs matches JAX"):
val rate = Tensor(Shape(Axis[A] -> 3)).fromArray(Array(1, 3, 10))
val rate = Tensor(Shape(Axis[A] -> 3)).fromArray(Array(1.0f, 3.0f, 10.0f))
val x = Tensor(Shape(Axis[A] -> 3)).fromArray(Array(1, 2, 8))

val dist = Poisson(rate)
Expand All @@ -413,7 +413,7 @@ class DistributionSuite extends DimwitTest:

it("sample means approximates rate"):
val poisson = Poisson(
Tensor(Shape(Axis[A] -> 2)).fromArray(Array(1, 5))
Tensor(Shape(Axis[A] -> 2)).fromArray(Array(1.0f, 5.0f))
)
val key = Random.Key(42)
val samples = key.splitvmap(Axis[Samples] -> 10000)(k => poisson.sample(k))
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