Graphics Programs Reference

In-Depth Information

You can see that over the 8 time steps, the arrival direction of the sound

has changed from

45 degrees to 30 degrees, and the two sources always

come from the same direction, strengthening our notion that the two are

in fact harmonics of the same source. Let us look at the time-frequency

and time-angle distributions of this data. The above output of the
whos

command shows that the row index of
data
corresponds to the different

angles, so if we calculate the mean over the rows we will be left with a

time-frequency distribution:

−

>> time_freq = mean(data);

>> size(time_freq)

ans =

1

1039

We are left with a 1

9 matrix of averages over the 128 arrival

angles. To plot the results we have to squeeze this to a two-dimensional

103

×

103

×

×

9 matrix:

time_freq = squeeze(mean(data));

imagesc(t,f,time_freq)

axis xy

xlabel('Time, s')

ylabel('Frequency, Hz')

The frequency varies slightly with time. By averaging the rows of the

data matrix we can get a similar plot of the variation of arrival angle

with time:

time_angle = squeeze(mean(data,2));

imagesc(t,th,time_angle)

axis xy

xlabel('Time, s')

ylabel('Arrival angle, degrees')

29.5 Multidimensional Cell Arrays

Multidimensional cell arrays are just like ordinary multidimensional

arrays, except that the cells can contain not only numbers, but vectors,