Error : Inner matrix dimensions must agree.

I'm getting an Error saying Inner matrix dimension must agree while trying to multipicate and plot

X = 2*cos(2*f1*pi*t)+sin(2*f2*pi*t)

Y = Ac*cos(Fc*2*pi*t)

Z = X*Y

I don't understand why i'm getting this error

Note : All the variables are defined in the code .

[Adam]

Debug and look at the sizes of each component in the workspace. Should be simple to find, but almost impossible just looking at that code from here.

[Alex Mcaulley]

Probably you want to do an element wise multiplication:

Z = X.*Y;

[Hussein Maher]

Here is the Code Mr Adam

                %  The Function We have choosen is m(t) = 2cos(100*pi*t)+sin(200*pi*t) %
   f1 = 50 ; 
   f2 = 100 ; 
  
                    %%Time specifications%%
   Fs =300;                   % samples per second
   Ts = 1/Fs ; 
   t = 0:Ts:1-Ts ;            % seconds per sample           
   Signal = 2*cos(2*f1*pi*t)+sin(2*f2*pi*t);

                   % ********** Part (1) ********** % 
                   % ****** Plotting Function ***** %
   subplot(212) ;
   plot(t,Signal);
   title('The signal') ;
   ylabel('V') ; 
   xlabel('time'); 
   
                   % Fourier Transform for Function %

   F = fft(Signal) ; 
   F_mag = abs(F) ; 
   U = Fs/length(F) ;
   Fx = -Fs/2:U:Fs/2-U;
   subplot(211);
   plot(Fx,F_mag/150) ; 
   title('Fourier Trasform of the function') ; 
   ylabel('F(f)') ; 
   xlabel('Frequency (Hz)') ; 

 %%%%%%%%%%%%%%%%%%%%%  DSB_LC %%%%%%%%%%%%%%%%%% 
 % Carrier % 
 Fc=70000 ; Ac = 1 ;  C = Ac*cos(Fc*2*pi*t) ; 
 m = 0.25 ;    %%Modulation INDEX (1)%%
 Y = (1+m*Signal)*Ac*cos(Fc*2*pi*t) ;
 subplot(210) ; 
 plot(t,Y) ;
 title('Modulated signal');
 ylabel('V'); 
 xlabel('time') ; 
 

Answer 1

[Image Analyst]

You forgot to give the actual error message! So we don't know which line it bombed on.

I agree with Adam and Alex though. Try .* and if that doesn't work, examine the sizes of all the variables. Of course you know that with a matrix multiplication with X*Y and X is rowsx*colsx and Y is rowsy * colsy, you must have colsx equal rowsy. For example [5*3] * [15*20] won't work but [5*3] * [3 * 20] will work because the inner dimensions are the same (unlike in your case).

Another thing to check is the shape. For example if X is a row vector and Y is a column vector (or vice versa) then multiplying them will not give a vector, even if they're the same length. Due to automatic expansion it will give a rectangular matrix.

tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

[Image Analyst]

Corrected code needs Y = (1+m*Signal) * Ac .* cos(Fc*2*pi*t)

Try this:

%  The Function We have choosen is m(t) = 2cos(100*pi*t)+sin(200*pi*t) %
f1 = 50 ;
f2 = 100 ;

%%Time specifications%%
Fs =300;                   % samples per second
Ts = 1/Fs ;
t = 0:Ts:1-Ts ;            % seconds per sample
Signal = 2*cos(2*f1*pi*t)+sin(2*f2*pi*t);
% ********** Part (1) ********** %
% ****** Plotting Function ***** %
subplot(2, 2, 1) ;
plot(t,Signal);
title('The signal') ;
ylabel('V') ;
xlabel('time');

% Fourier Transform for Function %
F = fft(Signal) ;
F_mag = abs(F) ;
U = Fs/length(F) ;
Fx = -Fs/2:U:Fs/2-U;
subplot(2, 2, 2);
plot(Fx,F_mag/150) ;
title('Fourier Trasform of the function') ;
ylabel('F(f)') ;
xlabel('Frequency (Hz)') ;
%%%%%%%%%%%%%%%%%%%%%  DSB_LC %%%%%%%%%%%%%%%%%%
% Carrier %
Fc=70000 ; Ac = 1 ;  C = Ac*cos(Fc*2*pi*t) ;
m = 0.25 ;    %%Modulation INDEX (1)%%
Y = (1+m*Signal) * Ac .* cos(Fc*2*pi*t) ;
subplot(2, 2, 3:4) ;
plot(t,Y) ;
title('Modulated signal');
ylabel('V');
xlabel('time') ;