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Secant Method

Secant Method. Civil Engineering Majors Authors: Autar Kaw, Jai Paul http://numericalmethods.eng.usf.edu Transforming Numerical Methods Education for STEM Undergraduates. Secant Method http://numericalmethods.eng.usf.edu. Secant Method – Derivation. Newton’s Method. (1).

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Secant Method

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  1. Secant Method Civil Engineering Majors Authors: Autar Kaw, Jai Paul http://numericalmethods.eng.usf.edu Transforming Numerical Methods Education for STEM Undergraduates http://numericalmethods.eng.usf.edu

  2. Secant Methodhttp://numericalmethods.eng.usf.edu

  3. Secant Method – Derivation Newton’s Method (1) Approximate the derivative (2) Substituting Equation (2) into Equation (1) gives the Secant method Figure 1 Geometrical illustration of the Newton-Raphson method. http://numericalmethods.eng.usf.edu

  4. Secant Method – Derivation The secant method can also be derived from geometry: The Geometric Similar Triangles can be written as On rearranging, the secant method is given as Figure 2 Geometrical representation of the Secant method. http://numericalmethods.eng.usf.edu

  5. Algorithm for Secant Method http://numericalmethods.eng.usf.edu

  6. Step 1 Calculate the next estimate of the root from two initial guesses Find the absolute relative approximate error http://numericalmethods.eng.usf.edu

  7. Step 2 Find if the absolute relative approximate error is greater than the prespecified relative error tolerance. If so, go back to step 1, else stop the algorithm. Also check if the number of iterations has exceeded the maximum number of iterations. http://numericalmethods.eng.usf.edu

  8. Example 1 You are making a bookshelf to carry books that range from 8 ½ ” to 11” in height and would take 29”of space along length. The material is wood having Young’s Modulus 3.667 Msi, thickness 3/8 ” and width 12”. You want to find the maximum vertical deflection of the bookshelf. The vertical deflection of the shelf is given by where x is the position where the deflection is maximum. Hence to find the maximum deflection we need to find where and conduct the second derivative test. http://numericalmethods.eng.usf.edu

  9. Example 1 Cont. The equation that gives the position x where the deflection is maximum is given by Figure 2 A loaded bookshelf. Use the secant method of finding roots of equations to find the position where the deflection is maximum. Conduct three iterations to estimate the root of the above equation. Find the absolute relative approximate error at the end of each iteration and the number of significant digits at least correct at the end of each iteration. http://numericalmethods.eng.usf.edu

  10. Example 1 Cont. Figure 3 Graph of the function f(x). http://numericalmethods.eng.usf.edu

  11. Example 1 Cont. Solution Let us take the initial guesses of the root of as and . Iteration 1 The estimate of the root is http://numericalmethods.eng.usf.edu

  12. Example 1 Cont. Figure 4 Graph of the estimated root after Iteration 1. http://numericalmethods.eng.usf.edu

  13. Example 1 Cont. The absolute relative approximate error at the end of Iteration 1 is The number of significant digits at least correct is 1, because the absolute relative approximate error is less than 5%. http://numericalmethods.eng.usf.edu

  14. Example 1 Cont. Iteration 2 The estimate of the root is http://numericalmethods.eng.usf.edu

  15. Example 1 Cont. Figure 5 Graph of the estimate root after Iteration 2. http://numericalmethods.eng.usf.edu

  16. Example 1 Cont. The absolute relative approximate error at the end of Iteration 2 is The number of significant digits at least correct is 2, because the absolute relative approximate error is less than 0.5%. http://numericalmethods.eng.usf.edu

  17. Example 1 Cont. Iteration 3 The estimate of the root is http://numericalmethods.eng.usf.edu

  18. Example 1 Cont. Figure 6 Graph of the estimate root after Iteration 3. http://numericalmethods.eng.usf.edu

  19. Example 1 Cont. The absolute relative approximate error at the end of Iteration 3 is The number of significant digits at least correct is 6, because the absolute relative approximate error is less than 0.00005%. http://numericalmethods.eng.usf.edu

  20. Advantages • Converges fast, if it converges • Requires two guesses that do not need to bracket the root http://numericalmethods.eng.usf.edu

  21. Drawbacks Division by zero http://numericalmethods.eng.usf.edu

  22. Drawbacks (continued) Root Jumping http://numericalmethods.eng.usf.edu

  23. Additional Resources For all resources on this topic such as digital audiovisual lectures, primers, textbook chapters, multiple-choice tests, worksheets in MATLAB, MATHEMATICA, MathCad and MAPLE, blogs, related physical problems, please visit http://numericalmethods.eng.usf.edu/topics/secant_method.html

  24. THE END http://numericalmethods.eng.usf.edu

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