The current implementation of the Next Reaction Method is very inefficient when the model contains assignment rules, which leads to extended calculation times.

There is a restriction regarding global quantities: If a differential equation is provided for a global quantity (the quantity is of type "ode") the model cannot be simulated stochastically with the current version of COPASI. If the global quantity is of type "assignment" stochastic simulation is possible but not as efficient as for models without assignments. No restrictions apply for "fixed" global quantities.

**Max Internal Steps**- This parameter is a positive integer value specifying the maximal number of internal steps the integrator is allowed to take before the next desired reporting time. The default value is '1000000'.

**Subtype**- This parameter is ignored in the current version of COPASI.

**Use Random Seed**- This flag can be '0' or '1' and determines if the user-defined random seed should be used for the calculation. The default is '0' meaning that the random seed is set to a random value before each run and consecutively calculated trajectories will be different. If the value of this flag is set to '1', the user-defined random seed will be used and each calculated trajectory will be the same for the same value of the given random seed.

**Random Seed**- This unsigned integer is used as random seed in the calculations, if the flag Use Random Seed is set to '1'. The default value is '1'.

This stochastic simulation method implements the Gillespie's direct method as described in [Gillespie76].

**Max Internal Steps**- This parameter is a positive integer value specifying the maximal number of internal steps the integrator is allowed to take before the next desired reporting time. The default value is '1000000'.

**Use Random Seed**- This flag can be '0' or '1' and determines if the user-defined random seed should be used for the calculation. The default is '0' meaning that the random seed is set to a random value before each run and consecutively calculated trajectories will be different. If the value of this flag is set to '1', the user-defined random seed will be used and each calculated trajectory will be the same for the same value of the given random seed.

**Random Seed**- This unsigned integer is used as random seed in the calculations, if the flag Use Random Seed is set to '1'. The default value is '1'.

This stochastic simulation method implements the τ-leap method as described in [Gillespie01]

**Max Internal Steps**- This parameter is a positive integer value specifying the maximal number of internal steps the integrator is allowed to take before the next desired reporting time. The default value is '10000'.

**Use Random Seed**- This flag can be '0' or '1' and determines if the user-defined random seed should be used for the calculation. The default is '0' meaning that the random seed is set to a random value before each run and consecutively calculated trajectories will be different. If the value of this flag is set to '1', the user-defined random seed will be used and each calculated trajectory will be the same for the same value of the given random seed.

**Random Seed**- This unsigned integer is used as random seed in the calculations, if the flag Use Random Seed is set to '1'. The default value is '1'.

This stochastic simulation method implements the Adaptive SSA/τ-leap Method as described in [Cao07]

**Max Internal Steps**- This parameter is a positive integer value specifying the maximal number of internal steps the integrator is allowed to take before the next desired reporting time. The default value is '10000000'.

**Use Random Seed**

**Random Seed**