How to calculate limit in n-number of times?

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Yanuar Rizki Pahlevi
评论： Yanuar Rizki Pahlevi 2020-9-6
Hi guys, I am working on a function which can generate the differentiation of equation given as input.
But I am trying to make it automatically given answer as input k. if k=1, then it will give the first differentiation, and so on.
and so I put dx^k on my code below, but matlab replied me with limit should be variable only. do you guys have any idea how to make it automatic?
function [Y_1,Y_2]=PolynomialDifferentiation (A,k)
syms x dx
Equation=poly2sym(A)
i=numel(A)
k=1:i-1
Equation_1=subs(Equation,x,(x+dx)); %to calculate F(x+dx)
Y=(Equation_1-Equation)/dx %(F(x+dx)-F(x))/dx
firstDiff=limit(Y,dx,0)%to define first differentiation of given equation
answer=coeffs(firstDiff)
secondEquation=firstDiff
C_1=subs(firstDiff,x,(x+dx));
D=(C_1-firstDiff)/dx;
secondDiff=limit(D,dx,0)
answer=coeffs(secondDiff)

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回答（1 个）

Matt J
Matt J 2020-9-6
编辑：Matt J 2020-9-6
I can't quite understand what your code is trying to do, but if you are trying to get the k-th derivative of a polynomial, given its coefficients A, you could just do
for i=1:k
A=polyder(A);
end
  1 个评论
Yanuar Rizki Pahlevi
Yanuar Rizki Pahlevi 2020-9-6
Hi, thank you for your response. Yes, i know i can use polyder, but I am trying to not use any polynomial equation at all.

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