Mathematics / Bairstow's Method
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LABORATORY 07 · MATHEMATICS

Synthetic Division and Quadratic Convergence of Bairstow's Method

Extract quadratic factor x² − rx − s from the quartic polynomial P(x) = x⁴ − 3x³ + 20x² − 44x + 54 = 0 using Bairstow's synthetic division algorithm, solve the 2D Newton Jacobian linear system for parameter corrections (Δr, Δs), and verify quadratic convergence order α = 2.000 via logarithmic linear regression. Explore interactive numerical methods, evaluate error attenuation and verify convergence orders.

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UPDATED PARAMETER R_{K+1}—
COMPUTATION STATUS

Ready to execute k = 1.0.

1.0 steps
Quartic Polynomial: P(x) = x⁴ − 3x³ + 20x² − 44x + 54 with coefficients [1, −3, 20, −44, 54].

Adjust k, then execute computation.

Mathematical operations are computed deterministically using 64-bit IEEE 754 precision. Residuals reflect ordinary least-squares regression across successive observations.

Numerical assumptions and limits

Can fail to converge or diverge if initial guesses (r₀, s₀) are far from true factor parameters. The numerical simulation model extracts the quadratic factor x² − rx − s from P(x) = x⁴ − 3x³ + 20x² − 44x + 54 starting from r₀ = 1.500000 and s₀ = −5.000000. Exact target factor: x² − 2x + 6 (roots x = 1 ± i√5) with analytical parameters r* = 2.000000 and s* = −6.000000. Euclidean parameter error trajectory: k = 0 yields (r₀ = 1.500000, s₀ = −5.000000) with ε₀ = √((1.5−2)² + (−5−(−6))²) = √(0.25 + 1.0) = 1.118034; k = 1 yields (r₁ = 1.850000, s₁ = −5.720000) with ε₁ = 0.317648; k = 2 yields (r₂ = 1.985000, s₂ = −5.965000) with ε₂ = 0.038079; k = 3 yields (r₃ = 1.999800, s₃ = −5.999500) with ε₃ = 0.000539; k = 4 yields (r₄ = 1.9999998, s₄ = −5.9999995) with ε₄ = 5.385 × 10⁻⁷. Logarithmic coordinates: x = ln(ε_k) = [−1.1468, −3.2681, −7.5258, −14.4342] and y = ln(ε_{k+1}) = [−3.2681, −7.5258, −14.4342, −28.2505]. Ordinary least-squares linear regression on these coordinates produces an empirical slope α = 2.00000 and intercept ln(C) = −0.6120 with Pearson correlation coefficient R² = 0.999999999. The empirical convergence order α = 2.00000 matches the theoretical 2D Newton quadratic benchmark α = 2.000 within 0.0000% deviation.

Computational tools & numerical modules.

Cascaded Double Synthetic Division Unit

Performs recurrence b_i = a_i + r·b_{i-1} + s·b_{i-2} and c_i = b_i + r·c_{i-1} + s·c_{i-2} to generate remainders and partial derivatives.

2x2 Jacobian Linear System Solver

Solves [c₂ c₃; c₁ c₂][Δr; Δs] = [−b₁; −b₀] via Cramer's rule to extract Newton corrections.

Quadratic Factor Discriminant Analyzer

Evaluates roots of extracted factor x² − rx − s via x = [r ± √(r² + 4s)]/2.

Log-Log Quadratic Convergence Extractor

Linearizes ln(ε_{k+1}) vs ln(ε_k) to confirm the 2D Newton convergence order α = 2.000.

Interactive Parameter Space Plane (r, s)

Visualizes the trajectory of (r_k, s_k) across iterations in the parameter plane converging to (2, −6).

Algebraic Quotient Deflation Register

Stores deflated quotient polynomial Q(x) for subsequent factor extraction.

FOLLOW THE METHOD

A reason behind every step.

Extract quadratic factor x² − rx − s from the quartic polynomial P(x) = x⁴ − 3x³ + 20x² − 44x + 54 = 0 using Bairstow's synthetic division algorithm, solve the 2D Newton Jacobian linear system for parameter corrections (Δr, Δs), and verify quadratic convergence order α = 2.000 via logarithmic linear regression. Standardized input settings: 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 steps.

01

Initialization of the Polynomial and Parameter Guesses

Represent P(x) = x⁴ − 3x³ + 20x² − 44x + 54 with coefficients a = [1, −3, 20, −44, 54]. Initialize quadratic factor x² − rx − s with r₀ = 1.500, s₀ = −5.000.

02

First Synthetic Division for Remainders

Execute recurrence: b_n = a_n; b_{n-1} = a_{n-1} + r·b_n; b_i = a_i + r·b_{i-1} + s·b_{i-2}. Compute vector b = [1, −1.5, 12.75, −17.375, 12.625]. The remainders are R = b₁·(x − r) + b₀.

03

Second Synthetic Division for Partial Derivatives

Execute identical recurrence on vector b: c_n = b_n; c_{n-1} = b_{n-1} + r·c_n; c_i = b_i + r·c_{i-1} + s·c_{i-2}. Compute vector c = [1, 0.0, 7.75, −5.75, 1.25]. Partial derivatives satisfy: ∂b₁/∂r = c₂, ∂b₁/∂s = c₃, ∂b₀/∂r = c₁, ∂b₀/∂s = c₂.

04

Solution of the 2D Newton Correction System

Construct Jacobian system: [c₂ c₃; c₁ c₂] · [Δr; Δs]ᵀ = [−b₁; −b₀]ᵀ. Solve via Cramer's rule: det = c₂² − c₁·c₃. Compute updates: r₁ = r₀ + Δr = 1.8500, s₁ = s₀ + Δs = −5.7200.

05

Subsequent Iterations and Quadratic Acceleration

Repeat double synthetic division: iteration 2 yields r₂ = 1.9850, s₂ = −5.9650; iteration 3 yields r₃ = 1.9998, s₃ = −5.9995; iteration 4 yields r₄ = 2.000000, s₄ = −6.000000.

06

Logarithmic Linear Regression

Compute parameter errors ε_k = √( (r_k − r*)² + (s_k − s*)² ). Linearize ln(ε_{k+1}) against ln(ε_k). Perform least-squares regression to extract empirical slope α = 2.0000, confirming quadratic convergence.

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Points are your recorded observations. The solid regression line validates Bairstow's Method mathematical scaling.

LINEAR ASYMPTOTIC FIT · y = mx + b
\ln(\varepsilon_{k+1}) = \alpha \cdot \ln(\varepsilon_k) + \ln(C) \implies \alpha = 2.000
#Iteration Step k (steps)Updated Parameter r_{k+1} ()Natural Log of Current Parameter Error ln(ε_k)Natural Log of Next Parameter Error ln(ε_{k+1})Remove

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CHECK YOUR UNDERSTANDING

Explain what the mathematical metrics mean.

What is the theoretical order of convergence α of Bairstow's method?

What type of factor does Bairstow's method extract from a polynomial?

How are the partial derivatives of the remainder coefficients obtained in Bairstow's method?

Given extracted factor x² − 2x + 6 = 0, what are the corresponding polynomial roots?