Add euler integrator description

wrappers/Python/doc/mod_roadrunner/cls_Integrator.rst

@@ -121,13 +121,14 @@ Gillespie
 
     RoadRunner's implementation of the standard Gillespie Direct Method SSA. The granularity of this simulator is individual molecules and kinetic processes are stochastic. Results will, in general, be different in each run, but a sufficiently large ensemble of runs should be statistically correct.
 
+    Can be used with the `r.gillespie function <https://libroadrunner.readthedocs.io/en/latest/api_reference.html?highlight=r%20gillespie#RoadRunner.RoadRunner.gillespie/>`_ or by setting integrator to gillespie (see below)
 
 .. attribute:: Integrator.initial_time_step
 
     Specifies the initial time step size. If inappropriate, CVODE will attempt to estimate a better initial time step. Default value is 0.0
 
     >>> r.setIntegrator('gillespie') # set integrator first
-    >>> r.integrator.seed = '1234'
+    >>> r.integrator.initial_time_step = 2
 
 
 .. attribute:: Integrator.maximum_time_step
@@ -154,11 +155,19 @@ Gillespie
 
     Perform a variable time step simulation. Enabling this setting will allow the integrator to adapt the size of each time step. This will result in a non-uniform time column. Default value is flase.
 
+Euler
+-----
+
+    The Euler method is one of the simplest approaches to solving a first order ODE. Given the rate of change of function f at time t, it computes the new value of f as ``f(t+h) = f(t) + h*f'(t)``, where h is the time step. Euler's method is rarely used in practice due to poor numerical robustness. Can be used with:
+
+    >>> r.setIntegrator('euler')
 
 RK4
 ---
 
-    Runge-Kutta methods are a family of algorithms for solving ODEs. They have considerably better accuracy than the Euler method. This integrator is a standard 4th order Runge-Kutta solver.
+    Runge-Kutta methods are a family of algorithms for solving ODEs. They have considerably better accuracy than the Euler method. This integrator is a standard 4th order Runge-Kutta solver. Can be used with:
+
+    >>> r.setIntegrator('rk4')
 
 
 RK45