How to apply window function in MATLAB

Hi

I wanna to apply a window function to my FT result. I have two questions, the first one is how to add the window function code, like w = window(blackman,L)? But it doesn't work. Another one is how to determine which window to choose? Here is my plots.

[dpb]

"Doesn't work" is completely non-descriptive.

What, specifically, makes you think the window function didn't "work"?

What did you do, specifically? Show code, not just a random phrase.

As for which to use, that's all dependent upon the point of the analysis and the type of input signal -- there is no firm, fixed answer.

Here's a link to a very introductory paper with links internally to more depth.

https://www.modalshop.com/rental/How-to-Choose-the-Best-FFT-Window-Function-for-an-Application?ID=1445

[Yian Chen]

Thanks,

My data is about temperature that shown on the plot. I wanna see the cycle of the temperature, but the temperature is osillated and the FT of it is like the plot above. How can I choose the window?

[dpb]

That doesn't indicate there is any real repetitive patter in the signal -- how did you get the above? As asked before, Show us the actual code used, we can't really tell anything at all from just the plot.

Most temperatures are slow-responding to external stimuli so you may not have collected nearly enough data to uncover any pattern.