changed vectors&matrices file, userguideUpdate branch

docs/user_guide/vectors_and_matrices.mdx

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+
+## Matrix Macros  
+
+#### matrix!
+Construct a fixed-size matrix directly from data. 
+
+This macro facilitates easy construction of matrices when the entries of the matrix are known (either as constants or expressions). 
+
+This macro produces an instance of `SMatrix`. This means that the data of the matrix is stored on the stack, and its dimensions are fixed at compile-time. If you want to construct a dynamic matrix, use `dmatrix!` instead.
+
+`matrix!` is intended to be both the simplest and most efficient way to construct (small) matrices, and can also be used in `const fncontexts`.
+
+The syntax is MATLAB-like. Column elements are separated by a comma (,), and a semi-colon (;) designates that a new row begins.
+
+```rust
+use nalgebra::matrix;
+
+// Produces a Matrix3<_> == SMatrix<_, 3, 3>
+
+let a = matrix![ 1, 2, 3;
+                4, 5, 6;
+                7, 8, 9];
+```
+
+You can also construct matrices with arbitrary expressions for its elements:
+
+```rust
+use nalgebra::{ matrix, Matrix2 };
+let theta = 0.45f64;
+let r = matrix![ theta.cos(), -theta.sin();
+                 theta.sin(),  theta.cos() ];
+```
+
+#### vector!  	
+
+Construct a fixed-size column vector directly from data. 
+
+Similarly to `matrix!`, this macro facilitates easy construction of fixed-size vectors. However, whereas the `matrix!` macro expects each row to be separated by a semi-colon, the syntax of this macro is instead similar to `vec!`, in that the elements of the vector are simply listed consecutively. 
+
+`vector!` is intended to be the most readable and performant way of constructing small, fixed-size vectors, and it is usable in `const fn` contexts.
+
+```rust 
+use nalgebra::vector;
+// Produces a Vector3<_> == SVector<_, 3>
+let v = vector![ 1, 2, 3 ];
+```
+
+#### point!
+Construct a fixed-size point directly from data. 
+
+Similarly to `vector!`, this macro facilitates easy construction of points.
+
+`point!` is intended to be the most readable and performant way of constructing small, points, and it is usable in `const fn` contexts.
+
+```rust
+use nalgebra::point;
+// Produces a Point3<_>
+let v = point![ 1, 2, 3 ];
+```
+
+#### dmatrix!
+Construct a dynamic matrix directly from data. The syntax is exactly the same as for `matrix!`, but instead of producing instances of `SMatrix`, it produces instances of `DMatrix`.
+
+At the moment it is not usable in `const fn` contexts.
+
+```rust
+use nalgebra::dmatrix;
+let a = dmatrix![ 1, 2, 3;                  
+                  4, 5, 6;                  
+                  7, 8, 9];
+```
+
+#### dvector! 
+Construct a dynamic column vector directly from data.
+
+The syntax is exactly the same as for `vector!`, but instead of producing instances of `SVector`, it produces instances of `DVector`. At the moment it is not usable in `const fn` contexts.
+
+```rust
+use nalgebra::dmatrix;
+let a = dvector![ 1, 2, 3];
+```