plot a sine wave of a vector

Hi,

I am new to Matlab and I am trying to plot a sine wave. All of the examples I have read don't seem to fit what I want to do so I thought I would ask for help here.

I am reading into a vector 1000 decinal numbers from a csv file. E.g. 1.23456,1.78987,1.04589 etc

Each number in the file represents the cumulation of 1 minute's worth of data so the whole file spans 1,000 minutes.

I am reading the file with the following command which populates the vector as expected.

records = csvread("data.txt");

I am now trying to plot a sinewave of these values but unfortunately I can't work it out so any help you can give would be very much appreciated

I need to end up with the following information. Amplitude, wavelength and frequency

Thanks,

John

[KSSV]

Why it can't work??? What problem you are facing?

[Rohit Anand]

Assuming that records is a vector and that you need to plot sin(records) vs. records you can easily do so using the plot command...

% For continuous plot
plot(records, sin(records));
% for discrete plot
stem(records, sin(records))

If this is not what you want, Please elaborate the issue further.

[John Skinner]

Hi and thanks for the response

Rohit, I did try to use the plot function but all I get is a straight line and I need to see the wave line. Sorry but I am not sure of the propper name for it.

This is the code that I have previously used which is that same as you suggested.

records = csvread("Data.txt");
plot(records, sin(records))

I have attached two jpg files with the output that I am getting and the output that I need.

If you look at straight.jpg then that is the result that I am getting.

If you look at wave.jpg then that is the result that I need

I have also attached the data file that I am using and also the script file that I have so far

Thanks again,

John

[Rohit Anand]

From what I can figure out is that You are trying to plot a sin of data that are too close to each other. Because of that you are not getting a sin curve per se. As There are not enough radians for si to complete a full cycle and it's value remains close to 0.9, hence the straight line.

As far as amplitude of the wave is concerned, plotiing this way you'll get the amplitude as 1.

As you're plotting sin(x) B It's max value will depend on range of x provided, for pi/2, it will be one.

And Frequency and Wavelength will also be constant in this case, based on the infromation you have provided.

One way like suggested below would be to use a fourier transform to extract information about different frequency components present in your line. But then again if it is a pure sine function that will not help you.

Answer 1

[Star Strider]

Try this:

y = load('Data.txt');
x = linspace(0, numel(y), numel(y));

figure
plot(x, y)
grid

It does not look a lot like a sine curve, however it is close enough. What information do you want from it?

.

[John Skinner]

Thanks Start Strider

What I eventually need to get from this data is the Amplitude of the wave, the wavelength and the frequency.

I am begining to wonder if what I need to do isn't even possible..

[Star Strider]

Itt’s likely possible, however much depends on what you want from the data. One option would be to use the detrend function before doing any other analyses (such as I have done here). Much depends on what your signal is, how you obtained it, and what liberties you can take with it.

Try this:

y = load('Data.txt');
x = linspace(0, numel(y), numel(y));
L = numel(y);
ym = y-mean(y);

Fs = 1/mean(diff(x));
Fn = Fs/2;
FTy = fft(ym)/L;
Fv = linspace(0, 1, fix(L/2)+1)*Fn;
Iv = 1:numel(Fv);

figure
loglog(Fv, abs(FTy(Iv))*2)
grid

That plots the Fourier transform of your signal, and from it, you can determine at least some of the information you want. (I used a loglog plot the make the low-frequency details more evident. Use plot to remove the logarithmic transformations.)

[John Skinner]

Hi Star Strider,

I am now examining this. I will get back to you with the ewsults

[Star Strider]

Great!

Waiting...