How can I remove negative values from vector (Half-Wave Rectification)

Question

jaylynn markey 2020-11-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/635559-how-can-i-remove-negative-values-from-vector-half-wave-rectification

回答： m.venkata manohar reddy 2021-8-1

I need help removing the negative values from a vector. I I started with an EMG signal and converted the signal from the time domain to the frequency domain using fft. Next I applied a bandpass filter from 25-400 Hz to get a filtered signal. Now I need to apply a half wave rectification. I would like to use a for loop to remove the ngative values from v_mag_filtered. I'd appreciate the help, I'm a bit rusty on MATLAB

% Time Signal

max_index = 10000;

freq = 960;

t_step = 1/freq;

for i = 1:max_index

t(i) = (i-1)*t_step;

v(i) = EMG(i) * 1E-6;

end

% Power spectrum

for i = 1:max_index

freq_range(i) = (1/t_step)*(i-1)/max_index;

end

v_freq = fft(v,max_index); %complex vector of ECG singal

v_mag = 2*v_freq.*conj(v_freq)/(max_index)^2; %phase information of complex number removed

x = freq_range(1:max_index/2);

y = v_mag(1:max_index/2);

%band pass filter

v_freq_filtered = v_freq;

for i = 1:max_index

if ((freq_range(i)<25))

v_freq_filtered(i) = 0.0;

end

if ((freq_range(i)>400))

v_freq_filtered(i) = 0.0;

end

v_mag_filtered = 2*v_freq_filtered.*conj(v_freq_filtered)/(max_index)^2;

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Answer 1

madhan ravi 2020-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/635559-how-can-i-remove-negative-values-from-vector-half-wave-rectification#answer_533274

在 MATLAB Online 中打开

 vector = [1, -1];
 vector( vector < 0 ) = 0 % [] to remove

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Answer 2

Star Strider 2020-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/635559-how-can-i-remove-negative-values-from-vector-half-wave-rectification#answer_533289

在 MATLAB Online 中打开

Try this:

t = linspace(0, 6*pi, 1E+5);
s = sin(t);
idx = s >= 0;                               % Conditional Logical Index
s_hwr = s.*idx;                             % Signal With Half-Wave Rectification
figure
plot(t, s_hwr)
grid
ylim([-1 1])

This will work regardless of your signal. Since ‘EMG’ is not provided, I use ‘s’ instead here.

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Charlotte Anderson 2020-11-4

Could you explain why you chose those values to input into the linspace function?

Star Strider 2020-11-4

Sure!

I chose 3 cycles

to provide a representative waveform, and

elements to produce a smooth plot. All of these (in this example) are arbitrary, so choose whatever values you want (within reason, and within the available memory capacity of your computer) to experiment with.

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