Added driver readme

README.md

@@ -9,7 +9,7 @@ not need to be adapted for a new situation are found in the `lib` folder. They a
 described in the following. Note that qualifiers, references and the like are discarded
 where it improves legibility. Consult the source files for more information.
 
-### Template Type `Vec2` (`vec2.hpp`), 2-vector utility class
+### Template Type `Vec2` (vec2.hpp), 2-vector utility class
 1. Template arguments
    - `value_t`: type of vector entries
 2. Members
@@ -46,7 +46,7 @@ where it improves legibility. Consult the source files for more information.
      - `[]` with `std::size_t`
      - `<<` with `std::ostream`
 
-### Type `Diagonalizer` (`diagonalizer.hpp`), class to diagonalize symmetric Matrices
+### Type `Diagonalizer` (diagonalizer.hpp), class to diagonalize symmetric Matrices
 1. Member functions
    - `std::vector<double> ev(std::vector<double> mat, size_t N)`
      - returns eigenvalues of the symmetric matrix mat of linear size N
@@ -57,7 +57,7 @@ where it improves legibility. Consult the source files for more information.
 2. Further developments
    - Only finding eigenvectors and -values in a certain range may be added later on
 
-### Template Type `Drum` (`drum.hpp`), represents a single drum top resonator
+### Template Type `Drum` (drum.hpp), represents a single drum top resonator
 1. Template arguments
    - `value_t`: Scalar type
    - `params_t`: Drum parameters container type
@@ -88,8 +88,11 @@ However, these containers likely need to be adapted to the situation at hand.
 When time evolving, the stepper will use the container of
 type `sbuffer_t` to store its intermediate results. Note that the default constructor of
 this class is `delete`'d. It should be constructed from an object of type `params_t`.
+5. Further developments
+Abstract interfaces for `params_t` and `vars_t` could be added, but they would
+be trivial.
 
-### Interface template type `Force` (`force.hpp`), force functional
+### Interface template type `Force` (force.hpp), force functional
 1. Template arguments
    - `value_t`: Scalar type
    - `params_t`: Drum parameters type
@@ -101,13 +104,44 @@ this class is `delete`'d. It should be constructed from an object of type `param
 3. Description
 This interface is a guide to complete implementation of a force functional. Any force
 functional should derive from this class, but the child type should then be used in
-order to avoid the vtable penalty. The type `drum_t` is a `Drum` with the given
+order to avoid the vtable penalty.
+
+The type `drum_t` is a `Drum` with the given
 template arguments. Typically, this functional would make heavy use of the `Drum`
 access members `get_parameters()` and `get_variables()`. The `time` argument of the
 functional exists to fit special cases as well. The file `include/force_simple.hpp`
 showcases how a real force functional could be written.
 
-### Template Type `Rk4Stepper` (`rk4_stepper.hpp`), performs timesteps using rk4 scheme
+### Interface template type `Driver` (driver.hpp), calculate drive of drums
+1. Template arguments
+   - `value_t`: Scalar type
+   - `drum_t`: Drum type
+2. Virtual functions
+   - `void precompute(value_t t_end, value_t dt, std::vector<drum_t> drum_vec)`
+     - Called once at begin of `system` lifetime
+   - `void step(value_t dt)`
+     - Move in time by `dt`
+   - `value_t operator()(size_t drum_index)`
+     - Returns drive of drum `drum_index` at current time
+3. Description
+This interface is a guide to complete implementation of a drive calculation class. Any drive
+class should derive from this class, but the child type should then be used in
+order to avoid the vtable penalty.
+
+The purpose of this class is to set the drive of each drum at specific times.
+
+In the `precompute` function, this class is passed all information it could need about
+the system. Hence it can in principle precompute all values for all drums and all times
+of the simulation.
+
+The member `step` is called to inform the `Driver` that time is advanced by the passed argument.
+Note that an rk4 scheme advances time in steps of `dt/2`.
+
+The functional should return the current drive on the drum with index passed as argument.
+
+An example implementation of a `Driver` is shown in `include/driver_simple.hpp`.
+
+### Template Type `Rk4Stepper` (rk4_stepper.hpp), performs timesteps using rk4 scheme
 1. Template arguments
    - `value_t`: Scalar type
    - `params_t`: Drum parameters container type