Hello, this is my first post in this site, so here goes:(adsbygoogle = window.adsbygoogle || []).push({});

Im working on a Matlab program. I have to calculate the second derivative of a given equation. The problem is that plotting the derivative is necessary, and that's where I'm stuck.

Here's what I've got so far:

% Evaluar f(x) y f'(x) usando diferencias hacia atras.

%

x = -10:0.1:10;

f = x.^3 - 5*x.^2 + 2*x + 8;

df = diff(f);

dx = diff(x);

df_dx = df./dx;

xd = x(2:length(x));

d2f = diff(f,2);

d2x = diff(f,2);

d2f_d2x = d2f./d2x;

%

% Graficar lo anterior.

%

subplot(2,1,1),...

plot(x,f,xd,df_dx,xd,d2f_d2x),...

title('Derivada de un polinomio de quinto grado'),...

xlabel('x'),grid,...

ylabel('f(x)'),...

axis([-4,5,-500,1500]);

On the internet I found out that diff(f,2) would calculate the second diff, I guess thats true. Ignore the spanish text :P.

When I try to run the program, the following appears:

??? Error using ==> plot

Vectors must be the same lengths.

Error in ==> C:\MATLAB6p5\work\segunda_diferencial.m

On line 16 ==> plot(x,f,xd,df_dx,xd,d2f_d2x),...

Hope you can help.

Thanks!

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# Matlab Second Derivative Ploting Problem

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