# Why does my plot of the Blackman window not match everyone else's in literature?

I've seen the plot for Blackman window as so in a bunch of books, as on this website: But plotting the same equation on Wolfram Alpha yields a different plot: Why is their graph not centered around 0? And why is their peak at y=1?

• You Wolfram query is wrong – msm Oct 30 '16 at 9:56
• SE.DSP wishes you a happy new year 2017, with a kind reminder that your question and its answers may require some action (update, votes, acceptance, etc.) – Laurent Duval Dec 31 '16 at 17:09
• Thanks @LaurentDuval. Action executed. Wish you a happy new year as well! – GrowinMan Jan 2 '17 at 22:31
• For some reason literature insists on defining window functions as between 0 and N-1, which I find unhelpful, the sinc function being zero-centred for instance. To make the Blackman window centred on 0 simply turn - 0.5 into + 0.5. – Michel Rouzic Dec 21 '18 at 22:29

There is a missing $$2\times$$ factor inside the second cosine, and you get a centered $$201$$ point windows with the change of variable $$x-100$$. See at Wolfram:
$$0.42 - 0.5*\cos\left(2\pi\frac{x-100}{200}\right) + 0.08 \cos\left(4\pi\frac{x-100}{200}\right)\,.$$