(version 0.1.1d, Windows 10)

I can not call function matmul() and matmul3d() directlly.

At the same time, they can be called as a method of Class userdata

a=vec(1,2,3)
b=vec(2,2,2)
matmul(a,b,1) -- runtime error, attempt to call a nil value (global 'matmul')
a:matmul(b,1) -- OK

Userdata methods aren't part of the global scope, they're part of the userdata's metatable. There's not all that much point in calling it directly, since matmul(a, b) can be replicated with a:matmul(b)

@Soupster

Well, I knew it.

What confused me was the way it was written in the manual:

matmul(m0, m1, [m_out])