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!

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Matlab Second Derivative Ploting Problem

**Physics Forums | Science Articles, Homework Help, Discussion**