Everybody to help me take a look at where the problem is
% give voice signal, respectively, and their respective different high frequency carrier signal multiplication, then get reuse signal
Fs=44100
Fc1=4000; Fc2=11000; Fc3=18000;
Y1=modulate (pyr1 fc1, fs, "FM"); Y1=FFT (Y1, n1);
Y2=modulate (pyr2 fc2, fs, "FM"); Y2=FFT (Y2, n2);
Y3=modulate (pyr3 fc3, fs, "FM"); Y3=FFT (Y3, n3);
Figure (2)
Subplot (3,1,1); The plot (abs (Y1)); Title (' after the signal is multiplied by 1 and carrier frequency spectrum diagram '); Xlabel (' frequency '); Ylabel (' margin ');
Subplot (3,1,2); The plot (abs (Y2)); Title (' signal spectrum carrier multiplication and since 2 '); Xlabel (' frequency '); Ylabel (' margin ');
Subplot (3,1,3); The plot (abs (Y3)); Title (' signal spectrum carrier multiplication and since 3 '); Xlabel (' frequency '); Ylabel (' margin ');
Figure (3)
Y=y1 y2 + + y3;
Stem (t, abs (FFT (Y)), '. '); Xlabel (' unit: Hz); Ylabel (' margin ');
The title (' reuse signal spectrum analysis)

Matrix dimensions must be consistent,

Error DSP11 (line 61)
Y=y1 y2 + + y3