update readme

Author: espdev

README.md

@@ -2,15 +2,22 @@
   <a href="https://github.com/espdev/csaps-rs"><img src="https://user-images.githubusercontent.com/1299189/76691347-0a5ac780-665b-11ea-99fa-bf4a0aea04dc.png" alt="csaps" width="400" /></a><br>
 </p>
 
-[![Build Status](https://travis-ci.org/espdev/csaps-rs.svg?branch=master)](https://travis-ci.org/espdev/csaps-rs)
-[![Coverage Status](https://coveralls.io/repos/github/espdev/csaps-rs/badge.svg?branch=master)](https://coveralls.io/github/espdev/csaps-rs?branch=master)
-
-:warning: :construction: **experimental**, **work-in-progress** :construction: :warning:
+<p align="center">
+<a href="https://travis-ci.org/espdev/csaps-rs"><img src="https://travis-ci.org/espdev/csaps-rs.svg?branch=master" alt="Build status" /></a>
+<a href="https://coveralls.io/github/espdev/csaps-rs?branch=master"><img src="https://coveralls.io/repos/github/espdev/csaps-rs/badge.svg?branch=master" alt="Coverage status" /></a>
+</p>
 
+<h4 align="center">
 Cubic spline approximation (smoothing) algorithm written in Rust.
+</h4>
+
+**csaps** is a crate for univariate, multivariate and n-dimensional grid data approximation using cubic smoothing splines.
+The package can be useful in practical engineering tasks for data approximation and smoothing.
 
 ## Usage
 
+Multivariate data smoothing
+
 ```rust
 use ndarray::{array, Array1};
 use csaps::CubicSmoothingSpline;
@@ -36,10 +43,52 @@ fn main() {
 }
 ```
 
+2-d grid (surface) data smoothing
+
+```rust
+use ndarray::array;
+use csaps::GridCubicSmoothingSpline;
+
+
+fn main() {
+    let x0 = array![1.0, 2.0, 3.0, 4.0];
+    let x1 = array![1.0, 2.0, 3.0, 4.0];
+    let x = vec![x0.view(), x1.view()];
+    
+    let xi0 = array![1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0];
+    let xi1 = array![1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0];
+    let xi = vec![xi0.view(), xi1.view()];
+    
+    let y = array![
+     [0.5, 1.2, 3.4, 2.5],
+     [1.5, 2.2, 4.4, 3.5],
+     [2.5, 3.2, 5.4, 4.5],
+     [3.5, 4.2, 6.4, 5.5],
+    ];
+    
+    let yi = GridCubicSmoothingSpline::new(&x, &y)
+     .make().unwrap()
+     .evaluate(&x).unwrap();
+    
+    println!("xi: {:?}", xi);
+    println!("yi: {}", yi);
+}
+ ```
+
+## Algorithms and implementations
+
+The crate implementation is based on [ndaray](https://github.com/rust-ndarray/ndarray) and 
+[sprs](https://github.com/vbarrielle/sprs) crates and has been inspired by Fortran routine SMOOTH from [PGS](http://pages.cs.wisc.edu/~deboor/pgs/) 
+(originally written by Carl de Boor).
+
+The implementation of the algotithm in other languages:
+ 
+- [csaps in Python](https://github.com/espdev/csaps) Python NumPy/SciPy based implementation
+- [csaps in C++](https://github.com/espdev/csaps-cpp) C++11 Eigen based implementation
+
 ## References
 
-- [csaps in Python](https://github.com/espdev/csaps)
-- [csaps in C++](https://github.com/espdev/csaps-cpp)
+- C. de Boor, A Practical Guide to Splines, Springer-Verlag, 1978.
 
 ## License