# rsparse
Provides a library for solving sparse linear systems using direct methods. This crate uses the algorithms from the book "Direct Methods For Sparse Linear Systems by Dr. Timothy A. Davis."
*Note: This library is a work in progress*
## Data structures
- CSC matrix (`Sprs`)
- Triplet matrix (`Trpl`)
## Features
- Convert from dense `Vec<Vec<f64>>` matrix to CSC sparse matrix `Sprs`
- Convert from sparse to dense `Vec<Vec<f64>>`
- Convert from a triplet format matrix `Trpl` to CSC `Sprs`
- Sparse matrix addition [C=A+B]
- Sparse matrix multiplication [C=A*B]
- Transpose sparse matrices
- Solve sparse linear systems
### Solvers
- **lsolve**: Solves a lower triangular system. Solves L*x=b. Where x and b are dense.
- **ltsolve**: Solves L’*x=b. Where x and b are dense.
- **usolve**: Solves an upper triangular system. Solves U*x=b. Solve Ux=b where x and b are dense
- **utsolve**: Solve U’x=b where x and b are dense
- **lusol**: A\b solved using LU factorization. Where A is `Sprs` and b is a dense vector
- **cholsol**: A\b solver using Cholesky factorization. *(Not yet available)*
- **qrsol**: A\b solver using QR factorization. *(Not yet available)*
## Examples
### Basic matrix operations
```rust
use rsparse;
fn main(){
// Create a CSC sparse matrix A
let a = rsparse::data::Sprs{
// Maximum number of entries
nzmax: 5,
// number of rows
m: 3,
//number of columns
n: 3,
// Values
x: vec![1., 9., 9., 2., 9.],
// Indices
i: vec![1, 2, 2, 0, 2],
// Pointers
p: vec![0, 2, 3, 5]
};
// Import the same matrix from a dense structure
let mut a2 = rsparse::data::Sprs::new();
a2.from_vec(
&vec![
vec![0., 0., 2.],
vec![1., 0., 0.],
vec![9., 9., 9.]
]
);
// Check if they are the same
assert_eq!(a.nzmax, a2.nzmax);
assert_eq!(a.m,a2.m);
assert_eq!(a.n,a2.n);
assert_eq!(a.x,a2.x);
assert_eq!(a.i,a2.i);
assert_eq!(a.p,a2.p);
// Transform A to dense and print result
println!("\nA");
print_matrix(&a.todense());
// Transpose A
let at = rsparse::transpose(&a);
// Transform to dense and print result
println!("\nAt");
print_matrix(&at.todense());
// B = A + A'
let b = rsparse::add(&a,&at,1.,1.); // C=alpha*A+beta*B
// Transform to dense and print result
println!("\nB");
print_matrix(&b.todense());
// C = A * B
let c = rsparse::multiply(&a, &b);
// Transform to dense and print result
println!("\nC");
print_matrix(&c.todense());
}
fn print_matrix(vec: &Vec<Vec<f64>>) { // source: https://stackoverflow.com/questions/36111784/how-to-convert-a-vecvecf64-into-a-string
for row in vec {
let cols_str: Vec<_> = row.iter().map(ToString::to_string).collect();
let line = cols_str.join("\t");
println!("{}", line);
}
}
```
Output:
```
A
0 0 2
1 0 0
9 9 9
At
0 1 9
0 0 9
2 0 9
B
0 1 11
1 0 9
11 9 18
C
22 18 36
0 1 11
108 90 342
```
### Solve a linear system
```rust
use rsparse;
fn main(){
// Arbitrary A matrix (dense)
let a = vec![
vec![8.2541e-01, 9.5622e-01, 4.6698e-01, 8.4410e-03, 6.3193e-01, 7.5741e-01, 5.3584e-01, 3.9448e-01],
vec![7.4808e-01, 2.0403e-01, 9.4649e-01, 2.5086e-01, 2.6931e-01, 5.5866e-01, 3.1827e-01, 2.9819e-02],
vec![6.3980e-01, 9.1615e-01, 8.5515e-01, 9.5323e-01, 7.8323e-01, 8.6003e-01, 7.5761e-01, 8.9255e-01],
vec![1.8726e-01, 8.9339e-01, 9.9796e-01, 5.0506e-01, 6.1439e-01, 4.3617e-01, 7.3369e-01, 1.5565e-01],
vec![2.8015e-02, 6.3404e-01, 8.4771e-01, 8.6419e-01, 2.7555e-01, 3.5909e-01, 7.6644e-01, 8.9905e-02],
vec![9.1817e-01, 8.6629e-01, 5.9917e-01, 1.9346e-01, 2.1960e-01, 1.8676e-01, 8.7020e-01, 2.7891e-01],
vec![3.1999e-01, 5.9988e-01, 8.7402e-01, 5.5710e-01, 2.4707e-01, 7.5652e-01, 8.3682e-01, 6.3145e-01],
vec![9.3807e-01, 7.5985e-02, 7.8758e-01, 3.6881e-01, 4.4553e-01, 5.5005e-02, 3.3908e-01, 3.4573e-01],
];
// Convert A to sparse
let mut a_sparse = rsparse::data::Sprs::new();
a_sparse.from_vec(&a);
// Generate arbitrary b vector
let mut b = vec![
0.4377,
0.7328,
0.1227,
0.1817,
0.2634,
0.6876,
0.8711,
0.4201
];
// Known solution:
/*
0.264678,
-1.228118,
-0.035452,
-0.676711,
-0.066194,
0.761495,
1.852384,
-0.282992
*/
// A*x=b -> solve for x -> place x in b
rsparse::lusol(&mut a_sparse, &mut b, 1, 1e-6);
println!("\nX");
println!("{:?}", &b);
}
```
Output:
```
X
[0.2646806068156303, -1.2280777288645675, -0.035491404094236435, -0.6766064748053932, -0.06619898266432682, 0.7615102544801993, 1.8522970972589123, -0.2830302118359591]
```
## Documentation
Documentation is available at [docs.rs](https://docs.rs/rsparse).