how can i calculate the derivative of an x vector?

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Paul Alequin 2018-9-5

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https://ww2.mathworks.cn/matlabcentral/answers/417741-how-can-i-calculate-the-derivative-of-an-x-vector

评论： madhan ravi 2018-9-6

Starts with an x vector created using linspace with a starting point of -5 and ends at +4 and at least 50 data points.

Evaluate the function f = 2x4 – 5x3 -12x2 + 30x +10 as a function of the MATLAB vector By hand, calculate the first derivative and then evaluate using the same x-vector. By hand, calculate the second derivative and then evaluate using the same x-vector.

Plot the three equations using different line color and different markers. You may use the extended plot command or roots.

Add a graph title, axes titles, and a legend.

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James Tursa 2018-9-5

What have you done so far? What specific problems are you having with your code? Do you know how to take the derivative of a polynomial by hand? Do you know how to evaluate polynomials in MATLAB?

Paul Alequin 2018-9-5

I don't know how to make this on matlab. I have my "by hand" calculate but i'm trying how to make this on the software.

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Answer 1

madhan ravi 2018-9-5

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https://ww2.mathworks.cn/matlabcentral/answers/417741-how-can-i-calculate-the-derivative-of-an-x-vector#answer_335628

编辑：madhan ravi 2018-9-5

在 MATLAB Online 中打开

Try the below:

syms f(x)
f = 2*x.^4 - 5*x.^3 -12*x.^2 + 30*x +10
first_derivative = diff(f)
second_derivative = diff(f,2)
%solved symbolically till here
%using numerical method from the above 
x=linspace(-5,4,50)
subplot(3,1,1)
plot(subs(x),subs(first_derivative),'*r-')
xlabel('x')
ylabel('first derivative')
title('1ST DERIVATIVE')
legend('FIRST DERIVATIVE')
subplot(3,1,2)
plot(subs(x),subs(second_derivative),'og-')
xlabel('x')
ylabel('second derivative')
title('2ND DERIVATIVE')
legend('SECOND DERIVATIVE')
subplot(3,1,3)
plot(subs(x),subs(f),'sqb-')
xlabel('x')
ylabel('equation')
title('FUNCTION')
legend('FUNCTION')