# how can i plot positive magnitude only of a sine wave

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ALI DRIDI on 4 Aug 2020
Commented: ALI DRIDI on 10 Aug 2020
i have been trying to plot the half positive of the sine wave without displaying the negative i couldnt find a way for it this is the function of the sine wave.
DC_Voltage = ((A) * sin((2)*(pi*F)*(T)+(Phase)));

KSSV on 4 Aug 2020
% get the index of only positive values
idx = DC_Voltage>=0 ;
plot(DC_Voltage(idx))

Sriram Tadavarty on 4 Aug 2020
Hi Ali,
From next time, please post the code you tried and where you have struck. So, that if one wants to try out the things, it helps to provide proper answer. Though you ask for plot of it, you haven't shown what is tried to plot for it.
I did take some possible values and tried to code what you are looking for.
A = 0.5;
F = 1000;
T = 0:1/(20*F):2/F;
Phase = 0;
DC_Voltage = ((A) * sin((2)*(pi*F).*(T)+(Phase)));
figure
plot(T,DC_Voltage)
% time stamps of DC_Voltage
DC_Voltage_Negative_Idx = DC_Voltage < 0;
DC_Voltage(DC_Voltage_Negative_Idx) = 0;
figure
plot(T,DC_Voltage)
% If you are not after the plot with T, then you can directly use plot(DC_Voltage(DC_Voltage >= 0))
Hope this helps.
Regards,
Sriram

#### 1 Comment

ALI DRIDI on 10 Aug 2020
for this coding it displays the positive mgnitude without the negative and i wanted to reverse the negative magnitude not = 0, but the plot(DC_Voltage(DC_Voltage >= 0)) is giving the plot of half time stamps of the original sine wave, when i add the 'T' for X axis it gives error message (error using plot vectors are not the same length. below is the output of plot(DC_Voltage(DC_Voltage >= 0)) without time stamp.