How to plot multiple graph

Hello all

I am going to plot f= sin(5x)/x^3 and its derivative f '(x) within the domain x ∈[0.1,0.4]using semilogy plot.

[Image Analyst]

OK.

[the cyclist]

Do you want two lines on the same plot, or do you want two plots (i.e. subplots).

[Nima Vali]

I want both (the function and its derivative) in one plot.

[Ameer Hamza]

This seems like a homework question. What have you already tried?

[Nima Vali]

clc; clear all; close all;

syms x

x=logspace(0.1,0.4);

f(x)=sin(5*x)./(x.^3);

Df=diff(f,x);

semilogx(x,f(x),'g')

hold on

semilogx(x,Df,'r')

grid

[Nima Vali]

but it comes with error

Answer 1

[Jon]

I don't have the symbolic toolbox, but I could get your code to work by modifying as follows. Note I did not include the line syms x as I don't have the symbolic toolbox.

x=logspace(0.1,0.4);
f =sin(5*x)./(x.^3);
Df= gradient(f)./gradient(x);
semilogx(x,f,'g')
hold on
semilogx(x,Df,'r')
grid

[Jon]

The key line is

Df= gradient(f)./gradient(x)

This gives a simple numerical approximation to the derivative.

You can see what the gradient function does by typing doc gradient on the command line.

[Nima Vali]

Yes, I get it. Thank you for help.

Answer 2

[Ameer Hamza]

You are using the symbolic variables incorrectly. Check this code

% clc; clear all; close all;
syms x
f(x)=sin(5*x)./(x.^3);
Df = diff(f,x);

xv = logspace(0.1,0.4);
semilogx(xv, f(xv), 'g')
hold on
semilogx(xv, Df(xv), 'r')
grid

[Nima Vali]

Yes Thank you for correction.

[Image Analyst]

And you might add a legend so you know what color is what.

legend('Original Signal', 'Derivative', 'Location', 'northeast');

[Nima Vali]

yes, Thank you.