How do I plot a signal over a duration of 1 second, with a = 200 and b = 0 for t<0.1 and a = 0 and b = 400 for t >=0.1

How do I produce a signal over a duration of 0.1 second at a sampling rate of 8kHz, with a = 1000 and b = 0 for t<0.05 and a = 0 and b = 1000 for t >=0.05

where the signal is x(t) = sin(2*pi*a*t) + sin(2*pi*b*t)

I have produced a similar signal prior to this, wherein a and b did not change value at certain points in time.

The similar signal:

%%Construct Signal
%       f_1(t) = sin(2*pi*a*t)+sin(2*pi*b*t)
% at a sampling rate of 8kHz, for a duration of 0.1 seconds
% a= 500 Hz
% b= 1000 Hz

fs = 8000; % Sampling Rate
ts = 1/fs; % Sampling Period
t = linspace(0, 0.1, 1001);
t = t(1:end-1);
a= 500;
b= 1000;

f_1 = sin(2*pi*a*t)+sin(2*pi*b*t); % function f_1(t)

figure(1)
plot(t,f_1);

Answer 1

[dpb]

Just define a and b over the range of length(t) as well and use the 'dot' operators in the evaluation...

a = 1000 and b = 0 for t<0.05 and a = 0 and b = 1000 for t >=0.05

a=zeros(size(t)); b=a;   % start w/ zero vectors
a(t<0.5)=1000;           % logical addressing of           
b(t>0.5)=1000;           % portions to set 
topi=2*pi;
f=sin(topi*a.*t)+sin(topi*b.*t);

ADDENDUM:

Your sample rate of 8 kHz is ignored in your formulation I note--if really want/need that instead of that used (altho it's marginally adequate as the plot will show) then use

t=0:ts:0.1;

instead of your linspace().