plot and axis function

I am confused about how plot and axis functions are used here. Normally, plot should be used as plot(time, ySound), but here plot(ySound) can work by itself. Why?

I understand that in axis([0 100 -1.1 1.1]), the first two digits actually represent the first 100 samples. However, shouldn't the first two digits of the axis function be used to represent the limits of the time?

sampleFreq = 8000;  freqMiddleC = 261.63;  amplitude = 1;
time = linspace(0, 2, sampleFreq * 2);  % Corresponds to 2 sec
ySound = amplitude * sin(2 * pi * freqMiddleC * time);
sound(ySound, sampleFreq); % Plays the sound
figure(1);
plot(ySound, 'o', .....    % Places a circle at each point
      'MarkerSize', 6, ...  % Make circle larger
      'MarkerFaceColor', 'r', 'MarkerEdgeColor', 'r');
axis([0 100 -1.1 1.1]); xlabel('time');

Thanks in advance,

- Lisa

Answer 1

[KL]

Take this simple example,

t = 1:10;
y = 10*t;

Now use just plot(y) in two ways to see the difference.

figure(1)
plot(y) %blue
hold on
plot(y(6:10)) %red

and now try to plot with x axis explicitly specified.

figure(2)
plot(t,y) %blue
hold on
plot(t(6:10),y(6:10)) %red

For the axis , it is,

axis([xmin xmax ymin ymax])

Answer 2

[Lisa Lee]

What I don't understand is why not axis([1 100 -1.1 1.1]) instead of axis([0 100 -1.1 1.1])? The default x array is the index number, which should start with 1. Am I right?

Answer 3

[Lisa Lee]

I got it now. Thank you so much!