MATLAB Function Finds The Derivative and Evaluates at Point A

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Sophie Culhane 2020-12-9

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https://ww2.mathworks.cn/matlabcentral/answers/688674-matlab-function-finds-the-derivative-and-evaluates-at-point-a

移动：Sabin 2023-1-15

My task is to write a MATLAB function that calculates the derivate of a polynomial, represented in vector form, and then also evaluates the derivative at a point a. So far I have the code to find the derivative, I just do not know how to evaluate at a from there. Note: f(x) = 3x^4 - 5x^2 -6x can be represented as P = [3, 0, -5, -6, 0]. Here is what I have so far:

function [PP,PPa] = ex5(P,a)

%

% where PP = the derivative of P

% PPa = the derivative of P evaluated at a

n = length(P);

PP = (n-1:-1:1).*P(1:n-1);

PPa = %not sure what to put here

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Sophie Culhane 2020-12-9

I am not able to use any of the specialized MATLAB commands such as “polyval” or “polyder”. Is there any other alternative to these commands I could try?

Steven Lord 2020-12-9

If I gave you a polynomial like

and asked you to evaluate it (by hand, with pencil and paper) at x = 4 how would you do that? List the steps, not just the answer. Can you adapt your pencil and paper technique into MATLAB code and use it to evaluate p = [1 2 3] at x = 4;?

Use polyval not as part of your implementation but to check your answer during development, comparing the result of your code to the results from polyval.

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