What does operator “dot” (.) mean?

The dot itself is not an operator, .^ is.

The .^ is a pointwise¹ (i.e. element-wise) power, as .* is the pointwise product.

.^
Array power. A.^B is the matrix with elements A(i,j) to the B(i,j) power. The sizes of A and B must be the same or be compatible.

C.f.

• “Array vs. Matrix Operations”: https://mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html
• “Pointwise”: http://en.wikipedia.org/wiki/Pointwise
• “Element-Wise Operations”: http://www.glue.umd.edu/afs/glue.umd.edu/system/info/olh/Numerical/Matlab_Matrix_Manipulation_Software/Matrix_Vector_Operations/elementwise

¹) Hence the dot.