Error in using diff for derivative

Anantha Krishna B

2022 1 18

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Hello

I am writing a function for calculating a root of a function using Newton's Method. In this i need to calculate value of derivative of the function. So I used diff but I am getting an error. I am thinking that the error is because diff only acts on symbolic functions and this somehow causes error. Is there any alternative way?

Below is my code

function [root] = Newton_rap_fun(a, error, f)
% function for newton's method
%   a is the initial approximation, error is the error tolerance given by
%   user
%   f is the given function
while (true)
    if (diff(f(a)) ~= 0)
         b = a - f(a)/diff(f(a));
         if (abs(b-a) <= error)
             root = b;
             break
         end
    else
         root = a;
    end    
end

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Anantha Krishna B 2022-1-19

@Torsten Thank you, this is a clever way. But is there any function that evaluates the derivative at point? I am asking because there will be some situations in which I need to evaluate higher order derivatives.