Shift data in the negative x direction then multiply shifted data with other plot

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monkey_matlab 2016-2-18

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https://ww2.mathworks.cn/matlabcentral/answers/268881-shift-data-in-the-negative-x-direction-then-multiply-shifted-data-with-other-plot

评论： Star Strider 2016-2-19

采纳的回答： Star Strider

data_1.csv

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Hello,

I have two plots from a simulated loop. I wanted to shift the data in plot 2 in the negative x direction, then multiply the shifted data with plot 1. How can I go about doing that? I have attached my data file.

Here is the code that I have so far:

% Read the file and store into matrix v
v=csvread('data_1.csv');
% Frequency vector
freq1 = v(:,1);
plot1 = v(:,2);
freq2 = v(:,3);
plot2 = v(:,4);
freq2_shifted = freq2*.5;
semilogx(freq1,plot1); 
ylim([-20 10]);
grid on;
hold on
semilogx(freq2,plot2);
semilogx(freq2_shifted,plot2);
legend('plot 1','plot 2','shifted');
hold off

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monkey_matlab 2016-2-19

编辑：monkey_matlab 2016-2-19

I actually wanted the shifted plot to look like that below. With the blue plot being shifted to the green plot's position, then multiplying the green plot and red plot together to get the "Product" plot. I was not sure how to approach this issue and led you down the wrong path of implementing the circshift function. Sorry and Thanks for your help.

Star Strider 2016-2-19

No worries.

See my Comment.

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Star Strider 2016-2-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/268881-shift-data-in-the-negative-x-direction-then-multiply-shifted-data-with-other-plot#answer_210366

The circshift function would be my approach, but I don’t know what you intend by ‘shift’.

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monkey_matlab 2016-2-19

OK, I see where the problem would be...If I multiply the frequency of plot 2 to get the green plot, the x data from plot 1 will not match the x data from the shifted plot. The first 10 points of the original plots and the shifted plots will be as follows:

Note that I cannot do a direct product now between plot 1 and shifted plot 2 as the x points do not line up now. Is there a way to line up the x points so that the shifted data has the same x values like plot 1? In the data below, I looked for the first number closest to 1 in column 5 and then copied the y-axis data to row 2, column 6 and so on, then copied the x-axis data from column 2. I then had the data as follows:

As you can see, I "fudged" the data to match up.

Is there an elegant way to generate the shifted data to have matching x-axis data points like the original plots so that a direct product can then be executed? Thanks for your time and help. I hope that I made it clear :-)

Star Strider 2016-2-19

My pleasure.

I am not certain how you shifted the frequencies, since you didn’t describe that. If you want to shift the data with respect to the frequencies, that would be easy: just do a circshift on the data, leaving the frequencies unshifted, then trim the last values from all records to eliminate the shifted value and last points from the other records. (An alternative would be to just trim the shifted data and then to use interp1 with the 'extrap' option to ‘create’ the missing shifted data. Your data are smooth enough to allow that.)

Or, you can shift the frequencies and keep the data unchanged. Your call.

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