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Matlab finding coefficients

  1. Sep 13, 2009 #1
    1. The problem statement, all variables and given/known data
    `Suppose it is known that the graph of the function y= ax^2 +bx^2+cx+d passes through four given points (x_i,y_i), i = 1,2,3,4. Write a user defined function that accepts these four points as input and computes the coefficients a,b,c and d. The function should solve four linear equations in terms of the four unknowns a,b,c,and d. Test your function for the case where (x_i,y_i) = (-2,-20), (0,4), (2,68), and (4, 508), whose answer is a = 7, b = 5, c = -6, and d = 4.

    2. Relevant equations

    3. The attempt at a solution
    Is there anything that can do something like a reverse polyval? Any ideas?
    Last edited: Sep 13, 2009
  2. jcsd
  3. Sep 14, 2009 #2


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    Replace each pair x_i, y_i in the equation. You will have four equations with the unknowns a, b, c, d.
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