error in matlab code

i want to add noise just in a part of signal

[houssem alimi]

figure(1)
subplot(121)
A1=1;A2=1;                  %amplitude of the signal
f1=1;f2=3;                  %frequency sinusoidal signal
Fs=100;                     %sampling rate        
Ts=1/Fs;                    %sampling period
fi=0;                       %phase shift
t=0:Ts:1;                   %time vector
y=A1*sin(2*pi*f1*t+fi)+A2*sin(2*pi*f2*t+fi);     %generated signal
plot(t(1:100),y(1:100),'k','LineWidth',2),grid on     
axis([0 1 -Inf Inf])
title('Addition deterministic and random signal','FontWeight','Bold','FontSize',14)
xlabel('time t(second)','FontWeight','normal','FontSize',12)
ylabel('amplitude u(volt)','FontWeight','normal','FontSize',12)
for t=0.4:0.01:0.5
    x(t)=y+awgn(y(t,5);
   end
 subplot(122)
plot(t,x,'k','LineWidth',2),grid on 
axis([0 1 -Inf Inf])

[KSSV]

for t=0.4:0.01:0.5
    x(t)=y+awgn(y(t,5);
   end

The above code is not correct.......you need to rethink on it.

[houssem alimi]

my goal is to add noise in a part of signal between t1 and t2

Answer 1

[KALYAN ACHARJYA]

Replace the complete for loop by following line

x=y+awgn(y,10);  % Here 10 represents SNR, change accordingly

No need of for loop for adding noise, awgn represents white Gaussian Noise

A1=1;A2=1;                  %amplitude of the signal
f1=1;f2=3;                  %frequency sinusoidal signal
Fs=100;                     %sampling rate        
Ts=1/Fs;                    %sampling period
fi=0;                       %phase shift
t=0:Ts:1;                   %time vector
y=A1*sin(2*pi*f1*t+fi)+A2*sin(2*pi*f2*t+fi);     %generated signal
subplot(121), plot(t(1:100),y(1:100),'k','LineWidth',2),grid on     
axis([0 1 -Inf Inf])
title('Addition deterministic and random signal','FontWeight','Bold','FontSize',14)
xlabel('time t(second)','FontWeight','normal','FontSize',12)
ylabel('amplitude u(volt)','FontWeight','normal','FontSize',12)
x=y+awgn(y,10);
subplot(122),plot(t,x,'k','LineWidth',2),grid on 
axis([0 1 -Inf Inf])

I didnot check the logic of the code. Hope it clered your error doubt.

The Reason of error, you use the for loop

for t=0.4:0.01:0.5

x(t)=.....,

which means x(0.4) is not allowed, array indxing should always in positive integer x(1), x(2)........

[houssem alimi]

i want that the noise is only appeared in a part of signal such between t1=0.4 and t2 = 0.5

[houssem alimi]

can you help me