Two Signals on one graph? Difference between two signals?

Question

Marwan 2011-7-21

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https://ww2.mathworks.cn/matlabcentral/answers/12104-two-signals-on-one-graph-difference-between-two-signals

评论： Walter Roberson 2017-5-24

Hello all;

I am working on two EEG signals (channel 5 & channel 13): f_c5(j,:) =abs(fft(t5(j,:),L)); f_c13(j,:) =abs(fft(t13(j,:),L));

And I am trying to find an equation that allow me to draw both signal on the same graph.

Also I would like to draw a graph presenting the difference between both of them.

Does anybody have any idea about it?

Many Thanks, Marwan

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Answer 1

the cyclist 2011-7-21

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在 MATLAB Online 中打开

Here are two ways.

x = 1:10;
y1 = 2*x;
y2 = 3.5*x;
% Multiple plot commands, with "hold" on
figure
hold on
plot(x,y1,'r');
plot(x,y2,'b');
plot(x,y2-y1,'g');
% Multiple lines in one plot command
figure
plot(x,y1,x,y2,x,y2-y1);

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Answer 2

Murthy 2011-9-14

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Hi.

What should we do when y1 and y2 are not defined on common x but different x values. Say x1= 1:10:100; and x2 = 0.1:0.05:300

How can I plot the difference of y1 and y2?

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Jan 2011-9-14

Simply fill the shorter of y1 or y2 with NaNs, such that both vectors have the same size again.

Walter Roberson 2011-9-14

Jan, if the x coordinates are not aligned on the same interval, subtraction is not going to be meaningful.

Murthy, you will need to interpolate (such as by using interp1()) to a common interval over the shared range and do the subtraction on the interpolated data. In the particular example you give, the interpolation could be done by subsampling of x2, x2(1*20:10*20:100*20) but it would be easy to construct examples where interp1() was needed.

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