# Multiplying sine wave with step function

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xRah on 5 Nov 2020
Answered: xRah on 5 Nov 2020
Hi again!
I'm trying to produce a sampled data vector of a sine wave with the following parameters:
• Amplitude 0.187
• Signal Freq. 187Hz
• Sampling rate 1600s^-1
I am running into an error and cannot figure out what the issue is with element wise multiplication of the step function and the sine wave. Code is as follows:
nn = -3:14; % index vector
uu = double(nn >= 0);% unit step
Ts = 1.6e-3;% sample time
Fs = 1600; % sample rate
t = linspace(-3, 14, Fs); % time
w = 2*pi*187; % omega
xx = 0.187*sin(w*t);% x(t) = 0.187sin(w*t)
xxuu = xx .* uu; % multiplying step function with sine wave
stem(t, xxuu)% stem plot
I am not entirely sure if this is the best way to go about this problem either. My code includes some hints I got from this site.

Ameer Hamza on 5 Nov 2020
Edited: Ameer Hamza on 5 Nov 2020
I am not sure how you defined 'uu' vector. But the following code works fine
Ts = 1.6e-3;% sample time
Fs = 1600; % sample rate
t = linspace(-3, 14, Fs); % time
uu = 1*(t>=0);
w = 2*pi*187; % omega
xx = 0.187*sin(w*t);% x(t) = 0.187sin(w*t)
xxuu = xx .* uu; % multiplying step function with sine wave
stem(t, xxuu)% stem plot
xRah on 5 Nov 2020
i seem to have forgotten it -.-

madhan ravi on 5 Nov 2020
uu = @(nn) +(nn >= 0);
xxuu = xx .* uu(t)

Paul on 5 Nov 2020
Change one line to:
xxuu = xx .* (t >= tstep); % set tstep as the time when the unit step is applied

xRah on 5 Nov 2020
Thank you all for your input and help :)