Exam 1(a) Fri 7 Oct 2005

  1. Consider a floating-point number system with base 10. There are five digits in the fraction (mantissa) and the exponents range between -7 and +8.
    1. What is the smallest positive floating-point number in this number system?
    2. What is the result of 12.381 + 0.098321 in this number system?
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  2. Derive the formula for the method of Aitken to accelerate the sequence x(k), k=0,1,...
    Illustrate the working of Aitken acceleration with a plot.
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  3. Below is the plot of g(x) = 0.4x^2 + 0.2x - 1.2. Starting at x(0) = 2.8, illustrate on the plot below how to produce three more points defined by x(k+1) = g(x(k)), k=0,1,...

    click here to see the plot

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  4. Consider f(x) = x^2 - 1.1 x + 0.18 over the interval [0,1].
    1. Starting with [0,1], apply two steps of the golden section search method, and indicate on the graph below where you do the function evaluations.
      In addition, mark the new intervals as [a1,b1], [a2,b2], and [a3,b3] on the x-axis.

      click here to see the graph

    2. Write the values for x1, x2, f(x1), and f(x2) (4 decimal places, scientific notation):
      +-------+------------+------------+------------+------------+
      | step  |     x1     |     x2     |    f(x1)   |    f(x2)   |
      +-------+------------+------------+------------+------------+
      |   0   |  3.820E-1  |  6.180E-1  |            |            |
      |   1   |            |            |            |            |
      |   2   |            |            |            |            |
      +-------+------------+------------+------------+------------+
      
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  5. Consider
                 [ -1.357E-01   6.112E-01   1.365E+00  ]
             A = [  8.797E-01   9.792E-01  -8.069E-01  ].
                 [ -2.263E-01  -1.160E+00   1.126E+00  ]
    
    1. Compute the LU decomposition of A with partial pivoting. Use 4 decimal places with rounding, and write all floating-point numbers in scientific format.
    2. What is the determinant of A?
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