diff --git a/content/pytorch/concepts/tensor-operations/terms/igamma/igamma.md b/content/pytorch/concepts/tensor-operations/terms/igamma/igamma.md new file mode 100644 index 00000000000..fc92876a068 --- /dev/null +++ b/content/pytorch/concepts/tensor-operations/terms/igamma/igamma.md @@ -0,0 +1,87 @@ +--- +Title: '.igamma()' +Description: 'Computes the lower incomplete gamma function for tensor inputs.' +Subjects: + - 'Computer Science' + - 'Data Science' + - 'Machine Learning' +Tags: + - 'AI' + - 'Deep Learning' + - 'Methods' + - 'PyTorch' + - 'Tensor' +CatalogContent: + - 'intro-to-py-torch-and-neural-networks' + - 'paths/data-science' +--- + +The **`torch.igamma()`** function in PyTorch computes the lower regularized incomplete gamma function, a special mathematical function often used in probability, statistics, and machine learning. `torch.igamma()` is an alias for `torch.special.gammainc()`. This means both functions compute the regularized lower incomplete gamma function and can be used interchangeably. + +## Syntax + +```pseudo +torch.igamma(input, other, *, out=None) +``` + +Or, alternatively: + +```pseudo +torch.special.gammainc(input, other, *, out=None) +``` + +**Parameters:** + +- `input` (Tensor): The shape parameter `a` of the Gamma function. +- `other` (Tensor): The upper limit `x` of the integral. +- `out` (Tensor, optional): The output tensor to store results. + +**Return value:** + +Returns a tensor containing the lower regularized incomplete gamma function values for each corresponding pair of elements in `input` and `other`. + +## Example 1: Basic Element-Wise Computation + +In this example, `torch.igamma()` computes the lower regularized incomplete gamma function for corresponding elements of two 1D tensors: + +```py +import torch + +a = torch.tensor([2.0, 3.0, 4.0]) +x = torch.tensor([1.0, 2.0, 3.0]) + +result = torch.igamma(a, x) +print(result) +``` + +This example produces the following output: + +```shell +tensor([0.2642, 0.3233, 0.3528]) +``` + +## Example 2: Gamma Distribution CDF + +In this example, `torch.igamma()` calculates the cumulative distribution function (CDF) of a Gamma distribution with shape ${a\}$ and rate 1: + +```py +import torch + +a = torch.tensor([2.0]) +x = torch.linspace(0, 5, 6) +gamma_cdf = torch.igamma(a, x) + +print(gamma_cdf) +``` + +The output of this code is: + +```shell +tensor([0.0000, 0.2642, 0.5940, 0.8009, 0.9084, 0.9596]) +``` + +The `.igamma()` function is useful for: + +- Computing CDFs of Gamma, Chi-square, or Exponential distributions. +- Performing Bayesian statistical modeling (priors and posteriors). +- Implementing neural network activations and loss functions involving special functions.