derivkit.calculus.calculus_core module#

Core utilities for calculus-based derivative computations.

This module provides shared helper functions for building derivative objects (gradients, Jacobians, Hessians, higher-order tensors) of scalar- and tensor-valued functions using DerivativeKit.

derivkit.calculus.calculus_core.component_scalar_eval(theta_vec: ndarray[tuple[Any, ...], dtype[float64]], *, function: Callable[[ArrayLike], float | ndarray], idx: int) → float#

Evaluates a single element of the model output function(theta_vec) as a scalar.

This helper is used internally when building derivatives of models that return multiple outputs (e.g. vectors or arrays). Derivative routines operate on scalar-valued functions, so one output component is selected and treated as a scalar function of the parameters.

Parameters:

  • theta_vec – 1D parameter vector.

  • function – Original function.

  • idx – Index of the output component to differentiate, where the output is first flattened with NumPy C-order (i.e. np.ravel(y, order="C")).

Returns:

Scalar value of the specified output component.

Raises:

IndexError – If idx is out of bounds for the model output.