Fitting a single amplitude sine wave to known peak/trough points

Hi again everyone,

I have a vector of data which I want to fit a sine wave to, I want the amplitude of the wave to remain constant though.

I have a script which finds the peaks and troughs in the original data (it is almost a sine wave on it's own) all I need to know is how to get Matlab to create a fixed amplitude sine wave between these known points. Alternatively Matlab could fit the wave to the original data, if that would be better.

I have searched for the answer but I think it's so simple most people don't have a problem. I have the signal processing and statistics toolboxes.

Thanks,

Rod.

An example of the data I have:

Raw data: https://docs.google.com/file/d/0B6rDEy3BkEW9S1hZNWxQUlpjZzg/edit?usp=sharing

Peak locations: https://docs.google.com/file/d/0B6rDEy3BkEW9Z0JFdnItZ0tjalk/edit?usp=sharing

Trough locations: https://docs.google.com/file/d/0B6rDEy3BkEW9V05rcXZsbGJwd2s/edit?usp=sharing

Answer 1

[Right Grievous]

I solved this problem by taking each location of a peak, using linspace to create the numbers 90-180 (as many numbers as I had time data points) between the peak and the next trough, then I did the same for between the trough and the next peak (180-270) and that peak and the next trough (270-360) and from that trough onto the next peak (360-450).

Then I subtracted 360 from any number over 360 to make all the values range from 0-360 in a correct sin function.

[M.A.G.]

I wonder if theres a more elegant solution