In fact, let's butcher the noise function for this display, so it generates wiggles only for the three circled grid points. Now you can see more clearly how the noise pattern is made.
The wiggles all have the same shape, but their orientations are pseudo-random. The exact orientations don't really matter - the important thing is that they are different and reasonably "random".
Now, what if we were to rotate these wiggles in place? Wouldn't that look cool?
To answer that shamelessly leading question: yes, it would, and this is what the parameter "alpha" does in the "psrdnoise" function. Each little wiggle is rotated by the same angle "alpha". This will change the noise pattern, but keep the wiggles pointing in different directions. (The "r" in "psrdnoise" is short for "rotating gradients".)
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