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NUMERICAL METHODS
Course Study Guide & Bisection Method
Prepared by:
REINNIEL JUNE AQUINO
Computer Engineering
Course Coverage
- Roots of Equations
- Systems of Linear Algebraic Equations
- Curve Fitting
- Differentiation
- Integration
- Ordinary Differential Equations
Note: This module focuses specifically on the first topic—Roots of Equations—using foundational bracketing algorithms.
Definition of Terms
- Numerical Methods: Techniques by which complex mathematical problems are formulated so that they can be solved
with arithmetic operations.
- Root: A value that makes the equation equal to zero. Visually, it is the exact coordinate where a plotted function crosses the
x-axis.
- Iteration: A repetitive process where the output of one sequence becomes the input of the next, gradually closing in on the
final answer.
- Bracketing: Identifying two initial guess values (a and b) that "trap" the root between them.
- Tolerance (ε): The acceptable margin of error. Since computers can calculate indefinitely, we set a tolerance (e.g., |f(x)| <
10 ⁻⁶) to tell the algorithm when to stop.
💡 Engineering Context: Analytical math (like factoring algebra) is great for paper, but computers only know
how to add, subtract, multiply, and divide. When the Ryzen 7 processor in your Laptop calculates complex game
physics, it can't use algebra. Instead, it uses numerical methods—brute-forcing arithmetic millions of times a
second to zero in on the exact answer.
Visualizing the Root:
Example Problem:
Use the bisection method to find the root of: f(x) = x - 2 + ln(x)
Solution:
Step 1: Let f(x) = 0 and set the tolerance to ε = 10 ⁻ ⁶ (0.000001).
Step 2: Find two initial values (a and b) that bracket the root.
Assume: a = 1 and b = 2
Evaluating f(x):
Because f(a) is negative and f(b) is positive, the sign-change condition is met.
Step 3 to 6: Iteration Table (Stopping Criterion: |f(x_m)| < 10 ⁻ ⁶)
💡 Scientific Notation: If you see a number like - 2.74E-05 in the table below, that is just computer-speak for
scientific notation. It means - 2.74 × 10 ⁻ ⁵, or - 0.0000274. It just means the number is getting incredibly close to
zero!
Iter # a x_m b f(a) f(x_m) f(b)
💡 Optional Bonus: How to Automate this in Excel
Nobody calculates 22 iterations by hand. Here is the exact logic to generate the table above in Excel in under 60 seconds:
A B C D E F
1 a x_m b f(a) f(x_m) f(b) 2 1 =(A2+C2)/2 2 =A2-2+LN(A2) =B2-2+LN(B2) =C2-2+LN(C2) 3 =IF(D2*E2<0, A2, B2)
=(A3+C3)/2 =IF(D2*E2<0, B2,
C2)
=A3-2+LN(A3) =B3-2+LN(B3) =C3-2+LN(C3)
- Row 2 (Initialization): Plug in your starting boundaries (A2, C2). The rest of the row uses formulas to find the midpoint and
evaluate the functions.
- Row 3 (The 'Sign-Change' Logic): This is the magic part. We use an IF statement to automatically decide which boundary
to keep based on the signs from the row above:
- Cell A3 checks if f(a) and f(x_m) have opposite signs (D2*E2 < 0). If True, the root is on the left, so we keep 'a' (A2). If False,
we swap 'a' for the midpoint (B2).
- Cell C3 checks the exact same thing (D2*E2 < 0). If True, the root is on the left, so 'b' doesn't change and we keep C2. If
False, the root is on the right, so we swap 'b' for the midpoint (B2).
- Automate: Highlight all of Row 3, grab the little green square in the bottom right corner, and drag it down to Row 25. Excel
will automatically step through the iterations.
Conclusion
The Bisection Method guarantees convergence as long as your initial guesses properly bracket the root. While it may take
more iterations to reach a tight tolerance compared to advanced methods (like Newton-Raphson), its absolute reliability
makes it a foundational tool in numerical analysis and computational engineering.