creating a figure that is a segment of another

i have a script that gives my figure(1) that graphs a cos wave over 5 sec then i need to section out the first second and have it display in figure(2). when i run my script i get the first figure and the second only displays the x,y cooridinates.

i think i have a problem in the way i sectioned the original vector.

my script looks like this:

clear;

clc;

close all;

% create vector of time values

t = 0.0 : 0.01 : 5.0;

% evaluate function at time points

f = 53*cos(104*pi*t).*exp(-1.35*t);

% plot t vs f(t)

figure(1) 

plot(t,f);

xlabel('t(sec)');

ylabel('f(t)');

%reindex t to exclude the last four seconds

t = 0.0 : 0.01 : 5;

%plot t vs f(t)

figure(2)

plot(t,f(t));

xlabel('t(sec)');

ylabel('f(t)');

Answer 1

[Sven]

I see a few problems:

Your f variable is still based on the original vector of t. You need to run:

f = 53*cos(104*pi*t).*exp(-1.35*t);

again, after you set your new t

Also, you have set t to be the same vector (ie, t = 0.0 : 0.01 : 5; ). I don't think you wanted this.

Finally, in the second figure you are calling:

plot(t,f(t));

but t is still a vector of times, not a vector of indices.

Perhaps you meant the following:

% First figure
t = 0.0 : 0.01 : 5.0;
f = 53*cos(104*pi*t).*exp(-1.35*t);
figure
plot(t,f);
xlabel('t(sec)');
ylabel('f(t)');

% Second figure, using only first 1/5th of t, f
idxs = 1:round(length(t)/5);
figure
plot(t(idxs),f(idxs));
xlabel('t(sec)');
ylabel('f(t)');

By the way, have you tried instead just:

set(gca,'xlim',[0 1])

You can run this after the first plot, and it will "zoom in" on only the first portion from 0 to 1 along the x axis. The rest will be excluded from view.

[SonOfAFather]

thank you the "idx( = 1:round(length(t)/5);" is what i had forgotten about.