numerical derivative in matlab
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Hi! How can I show the numerical value of the first derivative of a function in this code?
(-0.1*x^4) - (0.15*x^3) - (0.5*x^2) - (0.25*x) + 1.2
Enter Step Size:
0.5
Enter the point you want to approximate the Derivative:
0.5
clear
clc
format short
syms x
P=input ('Enter the Equation: ','s');
f=inline(P)
g=diff(f(x),x);
h=input ('Enter Step Size: ')
x=input ('Enter the point you want to approximate the Derivative: ')
fprintf('f(x) = %0.4f', f(x))
dy=g(x) % How Can I get the derivative equation of g in numerical answer by substituting the value of x?
fprintf('x(xi+1) = %0.4f', x+(1*h))
fprintf('f(xi+1) = %0.4f', f(x+(1*h)))
FDD=(f(x+(1*h))-f(x))/h;
fprintf('FDD (Truncated) = %0.4f', (f(x+(1*h))-f(x))/h)
2 commentaires
Torsten
le 4 Août 2022
dy = subs(g,x,x0)
if you rename x in x0 in the preceeding input-command for x.
Dyuman Joshi
le 5 Jan 2024
Réponses (1)
Ayush
le 5 Jan 2024
Modifié(e) : Ayush
le 5 Jan 2024
Hi Christoppe,
I understand that you want to show the numerical value of the first derivative of a function in the given code.
To do so, you need to substitute the value of “x” into the derivative function “g” and then evaluate it. This can be done by using the “subs” function or by converting the symbolic expression to a function and then evaluating it at the given point.
Refer the modified code below for better understanding:
clear
clc
format short
syms x
% P = input('Enter the Equation: ','s');
P = (-0.1*x^4) - (0.15*x^3) - (0.5*x^2) - (0.25*x) + 1.2;
f = inline(P);
g = diff(f(x),x);
% h = input('Enter Step Size: ');
h = 0.5;
% x_val = input('Enter the point you want to approximate the Derivative: ');
x_val = 0.5;
fprintf('f(x) = %0.4f\n', f(x_val)); % Display the value of the function at x
% Calculate the numerical value of the derivative at x
g_val = double(subs(g, x, x_val));
fprintf('g(x) = %0.4f\n', g_val); % Display the numerical value of the derivative
fprintf('x(xi+1) = %0.4f\n', x_val + h);
fprintf('f(xi+1) = %0.4f\n', f(x_val + h));
FDD = (f(x_val + h) - f(x_val)) / h;
fprintf('FDD (Truncated) = %0.4f\n', FDD);
The "inline" function is not recommended, instead use the "anonymous function". For more information on the “subs” function and "anonymous function" refer the documentation page given below:
- "subs function": https://www.mathworks.com/help/symbolic/subs.html
- "anonymous function": https://www.mathworks.com/help/matlab/matlab_prog/anonymous-functions.html
Regards,
Ayush
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