# Skill 042

> High-performance numerical computing and machine learning workflows using JAX. Supports array operations, automatic differentiation, JIT compilation, RNN-style scans, map/reduce operations, and gradient computations. Ideal for scientific computing, ML models, and dynamic array transformations.

- Skill: `legendtkl/skill-042` (Agent Skill)
- Install (CLI): `npx skillmds@latest add legendtkl/skill-042`
- Raw SKILL.md: https://api.skillmd.com/api/skills/legendtkl/skill-042/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- License: Proprietary. LICENSE.txt has complete terms
- Author: legendtkl (https://skillmd.com/u/legendtkl)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/legendtkl/skill-042

---


# Requirements for Outputs

## General Guidelines

### Arrays
- All arrays MUST be compatible with JAX (`jnp.array`) or convertible from Python lists.
- Use `.npy`, `.npz`, JSON, or pickle for saving arrays.

### Operations
- Validate input types and shapes for all functions.
- Maintain numerical stability for all operations.
- Provide meaningful error messages for unsupported operations or invalid inputs.


# JAX Skills

## 1. Loading and Saving Arrays

### `load(path)`
**Description**: Load a JAX-compatible array from a file. Supports `.npy` and `.npz`.  
**Parameters**:
- `path` (str): Path to the input file.  

**Returns**: JAX array or dict of arrays if `.npz`.

```python
import jax_skills as jx

arr = jx.load("data.npy")
arr_dict = jx.load("data.npz")
```

### `save(data, path)`
**Description**: Save a JAX array or Python array to `.npy`.
**Parameters**:
- data (array): Array to save.
- path (str): File path to save.

```python
jx.save(arr, "output.npy")
```
## 2. Map and Reduce Operations
### `map_op(array, op)`
**Description**: Apply elementwise operations on an array using JAX vmap.
**Parameters**:
- array (array): Input array.
- op (str): Operation name ("square" supported).

```python
squared = jx.map_op(arr, "square")
```

### `reduce_op(array, op, axis)`
**Description**: Reduce array along a given axis.
**Parameters**:
- array (array): Input array.
- op (str): Operation name ("mean" supported).
- axis (int): Axis along which to reduce.

```python
mean_vals = jx.reduce_op(arr, "mean", axis=0)
```

## 3. Gradients and Optimization
### `logistic_grad(x, y, w)`
**Description**: Compute the gradient of logistic loss with respect to weights.
**Parameters**:
- x (array): Input features.
- y (array): Labels.
- w (array): Weight vector.

```python
grad_w = jx.logistic_grad(X_train, y_train, w_init)
```

**Notes**:
- Uses jax.grad for automatic differentiation.
- Logistic loss: mean(log(1 + exp(-y * (x @ w)))).

## 4. Recurrent Scan
### `rnn_scan(seq, Wx, Wh, b)`
**Description**: Apply an RNN-style scan over a sequence using JAX lax.scan.
**Parameters**:
- seq (array): Input sequence.
- Wx (array): Input-to-hidden weight matrix.
- Wh (array): Hidden-to-hidden weight matrix.
- b (array): Bias vector.

```python
hseq = jx.rnn_scan(sequence, Wx, Wh, b)
```

**Notes**:
- Returns sequence of hidden states.
- Uses tanh activation.

## 5. JIT Compilation
### `jit_run(fn, args)`
**Description**: JIT compile and run a function using JAX.
**Parameters**:
- fn (callable): Function to compile.
- args (tuple): Arguments for the function.

```python
result = jx.jit_run(my_function, (arg1, arg2))
```
**Notes**:
- Speeds up repeated function calls.
- Input shapes must be consistent across calls.

# Best Practices
- Prefer JAX arrays (jnp.array) for all operations; convert to NumPy only when saving.
- Avoid side effects inside functions passed to vmap or scan.
- Validate input shapes for map_op, reduce_op, and rnn_scan.
- Use JIT compilation (jit_run) for compute-heavy functions.
- Save arrays using .npy or pickle/json to avoid system-specific issues.

# Example Workflow
```python
import jax.numpy as jnp
import jax_skills as jx

# Load array
arr = jx.load("data.npy")

# Square elements
arr2 = jx.map_op(arr, "square")

# Reduce along axis
mean_arr = jx.reduce_op(arr2, "mean", axis=0)

# Compute logistic gradient
grad_w = jx.logistic_grad(X_train, y_train, w_init)

# RNN scan
hseq = jx.rnn_scan(sequence, Wx, Wh, b)

# Save result
jx.save(hseq, "hseq.npy")
```
# Notes
- This skill set is designed for scientific computing, ML model prototyping, and dynamic array transformations.

- Emphasizes JAX-native operations, automatic differentiation, and JIT compilation.

- Avoid unnecessary conversions to NumPy; only convert when interacting with external file formats.