Add Prerequisites page

Author: ikorotkin

docs/prerequisites.md

@@ -0,0 +1,32 @@
+---
+title: Prerequisites
+layout: default
+nav_order: 1.7
+---
+
+# Prerequisites
+
+## `dae-cpp` header file
+
+The main header file of the library is `dae-cpp/solver.hpp`. It contains all the necessary classes, solvers, and utilities. To include `dae-cpp` into the project, use
+
+```cpp
+#include <dae-cpp/solver.hpp>
+```
+
+## `dae-cpp` namespace
+
+All classes and solvers exposed to the user are defined in the `daecpp` namespace. This means that all names from the `dae-cpp` library should be prefixed with `daecpp::`. Alternatively, use
+
+```cpp
+using namespace daecpp;
+```
+
+## `dae-cpp` types
+
+| Type | Equivalent to | Note |
+| ---- | ------------- | ---- |
+| `daecpp::int_type` | `uint32_t` (default), <br> `uint64_t` if `DAECPP_LONG` is defined | Unsigned integer type, used for sparse matrix indices |
+| `daecpp::float_type` | `double` (default), <br> `float` if `DAECPP_SINGLE` is defined | Floating point scalar, used for sparse matrix coefficients |
+| `daecpp::state_vector` | `std::vector<float_type>` | State vector, used, for example, to define the initial condition |
+| `daecpp::state_type` | `autodiff::VectorXreal` | State vector, used for the [vector function](vector-function.html) definition so that it can be automatically (algorithmically) differentiated using `autodiff` package |

docs/sparse-matrix.md

@@ -7,8 +7,8 @@ nav_order: 2
 # Sparse Matrix class
 
 Sparse Matrix class `daecpp::sparse_matrix` defines sparse matrix holder in [three-array format](#three-array-format). 
-It is used to define the mass matrix and, optionally, the Jacobian matrix of the DAE system.
-The class provides a set of helper tools for the user to allocate memory, define and convert sparse matrices in a very straightforward way, e.g.:
+It is used to define the [mass matrix](mass-matrix.html) and, optionally, the [Jacobian matrix](jacobian-matrix.html) of the DAE system.
+The class provides a set of helper tools for the user to allocate memory, define and convert sparse matrices, etc., in a very straightforward way, e.g.:
 
 ```cpp
 sparse_matrix M;                 // Creates empty sparse matrix M