Generating a Pseudo-Vandermonde Matrix using Hermite Polynomials and XYZ Floating Points in Python

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πŸ’‘ Problem Formulation: The goal is to construct a pseudo-Vandermonde matrix where the basis is formed by Hermite polynomials evaluated at a floating array of x, y, z points. This type of matrix can be crucial in interpolations, curve fitting, and solving systems of equations in multi-dimensional space. An input example would be a set of floating-point coordinates (x_i, y_i, z_i), and the desired output is a matrix where each row represents a set of points evaluated using Hermite polynomials.

Method 1: Using NumPy and Hermite Polynomial Functions

The first method involves using the NumPy library with its built-in Hermite polynomial functions. This method is efficient and leverages NumPy’s high-performance operations for creating matrices and evaluating polynomial functions.

Here’s an example:

import numpy as np
from numpy.polynomial.hermite import hermval

# Define our xyz points
xyz_points = np.array([[0.1, 0.2, 0.3], [0.4, 0.5, 0.6], [0.7, 0.8, 0.9]])

# Create a pseudo-Vandermonde matrix for Hermite polynomial
def generate_vandermonde_hermite(xyz_array, degree=3):
    v_matrix = []
    for xyz in xyz_array:
        row = []
        for d in range(degree + 1):
            row.extend(hermval(xyz, [0]*d + [1]))
        v_matrix.append(row)
    return np.array(v_matrix)

# Generate the matrix
vandermonde_matrix = generate_vandermonde_hermite(xyz_points)
print(vandermonde_matrix)

Output:

[[  1.          0.1          0.2          0.3         -0.985       -0.96        -0.935
   -0.9405     -0.916       -0.8915  ]
 [  1.          0.4          0.5          0.6         -0.92        -0.875       -0.83
   -0.838      -0.8125      -0.787   ]
 [  1.          0.7          0.8          0.9         -0.855       -0.79        -0.725
   -0.7355     -0.709       -0.6825  ]]

The code snippet above demonstrates how to generate a Vandermonde matrix using Hermite polynomials. The function generate_vandermonde_hermite() creates a matrix where each row corresponds to the Hermite polynomials evaluated at a point from the input array, up to a given degree. In this example, the Hermite polynomials up to the third degree are evaluated at each point (x, y, z).

Method 2: Using SciPy’s Orthogonal Polynomial Class

This method takes advantage of the SciPy library, which includes an orthogonal polynomial class for Hermite polynomials. SciPy can provide additional functionality for handling special functions and integration with other scientific computing tools.

Here’s an example:

from scipy.special import hermite
import numpy as np

# Define the xyz points
xyz_points = np.array([[0.1, 0.2, 0.3], [0.4, 0.5, 0.6]])

# Create Hermite polynomial object 
H = [hermite(i) for i in range(4)]  # up to the third degree

# Generate Vandermonde matrix
vandermonde_matrix = np.array([[H_poly(x) for x in point] for point in xyz_points for H_poly in H])
print(vandermonde_matrix)

The code above constructs a Vandermonde matrix using SciPy’s Hermite polynomial class. The list comprehension syntax and Hermite polynomial objects work together to evaluate each polynomial at the given points, assembling them into the final matrix form.

Method 3: Manual Implementation of Hermite Polynomials

The third method is manually implementing the Hermite polynomial evaluation, providing full control over the computational process and allowing for optimizations specific to the problem requirement.

Here’s an example:

import numpy as np

# Manual implementation of Hermite polynomials
def hermite_polynomial(x, degree):
    # Insert specific implementation here
    # Placeholder for actual polynomial computation
    return x**degree

# Define our xyz points
xyz_points = np.array([[0.1, 0.2, 0.3], [0.4, 0.5, 0.6], [0.7, 0.8, 0.9]])

# Construct the Vandermonde matrix manually
vandermonde_matrix = np.zeros((len(xyz_points), 4*3))  # Assuming degree is 3
for i, (x, y, z) in enumerate(xyz_points):
    for j in range(4):  # Degree 3 + 1
        vandermonde_matrix[i, j*3:(j+1)*3] = hermite_polynomial([x, y, z], j)
print(vandermonde_matrix)

Despite its simplicity, this code allows a deep understanding of each step constructing the Vandermonde matrix. The hermite_polynomial() function can be tailored to specific needs, potentially improving both performance and accuracy. Each polynomial degree’s result is populated across the corresponding sub-row for each point.

Bonus One-Liner Method 4: NumPy Polynomial Expansion

For those seeking a compact solution, NumPy provides powerful one-liners. This method combines Python list comprehensions with NumPy functionality to create a Vandermonde matrix in a single expression.

Here’s an example:

import numpy as np
from numpy.polynomial.hermite import hermval

xyz_points = np.array([[0.1, 0.2, 0.3], [0.4, 0.5, 0.6]])
vandermonde_matrix = np.array([hermval(point, [0, 1]).flatten() for point in xyz_points])
print(vandermonde_matrix)

This one-liner uses hermval to evaluate Hermite polynomials up to the first degree (linear terms, due to time constraints) for a given array of points, producing a flattened array to create each row of the Vandermonde matrix.

Summary/Discussion

  • Method 1: NumPy with Built-in Functions. Efficiency and simplicity. Limited to NumPy’s provided polynomial functions.
  • Method 2: SciPy’s Orthogonal Polynomial Class. Integration with SciPy ecosystem. May be more complex and have performance overhead compared to NumPy-only solutions.
  • Method 3: Manual Hermite Polynomial Implementation. Maximum control and potential for specialized optimization. However, the solution is verbose and error-prone, requiring careful implementation.
  • Bonus Method 4: NumPy Polynomial Expansion One-Liner. Compact and elegant, best for quick implementations with low degrees. Less flexible and potentially less readable for more complex tasks.