Exam 2(c) Mon 1 Apr 2002

  1. Consider the polynomial p(x) = x^2 - x + 1.

    1. Construct the Newton form of p(x) by divided differences, using the points (x_i,p(x_i)), with x_i = i, for i=0,1,2,3.

    2. Explain why the last element f_0123 in the table of divided differences you constructed above is (or should have been) zero.
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  2. The Maclaurin expansion of sqrt(x+1) is
    
                       2         3          4          5    21   6    33   7
      1 + 1/2 x - 1/8 x  + 1/16 x  - 5/128 x  + 7/256 x  - ---- x  + ---- x  
                                                           1024      2048
    
             429   8    715   9      10
         -  ----- x  + ----- x  + O(x  )
            32768      65536
    
    
    Use this Maclaurin expansion to construct a Padé approximation for sqrt(x+1) as a quotient of two quadrics.
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  3. Give the continued-fraction representation for x/(x^2 - 7).
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  4. Use central differences and Richardson extrapolation to compute a sixth order approximation for the derivative of arccos(x) at x = 0.7.

    1. Start with h=0.1 and divide h by 2 (i.e.: r = 1/2) to build the first column of the extrapolation table. Show how you applied the formulas (for partial credit). Write your answers with ten decimal places.

    2. How many decimal places are correct in your final answer from Richardson extrapolation? Explain.
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  5. Consider the quadrature rule
                  2a
                 /               
                |   f(x) dx  = w  f(-a) + w  f(a)   for a > 0.
                /               1          2 
                 -2a
    
    Determine the weights w_1 and w_2 so that the rule has the highest possible algebraic degree of precision.
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  6. How would you compute a least squares approximation using Chebyshev polynomials? For example, suppose we have five samples (x_i,y_i), i=1,2,...,5. We wish to fit the data with a second degree polynomial p(x) = a_0 T_0(x) + a_1 T_1(x) + a_2 T_2(x). Describe how you would find the coefficients a_0, a_1, and a_2.
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