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Product form stationary distributions of stochastic reaction - PowerPoint PPT Presentation

Product form stationary distributions of stochastic reaction networks, and application to constrained averaging of multiscale systems Simon Cotter University of Manchester 19th July 2016 Simon Cotter Product form stationary dist. 0 / 35


  1. QSSA: Simple Example k 2 k 4 / ( k 2 + k 3 ) s k 1 ∅ − − − − → S − − − − − − − − − → ∅ Quantify error by computing error in invariant distribution of S = X 1 + X 2 � k 1 ( k 2 + k 3 ) � S ( ∞ ) ∼ P (QSSA approximation) k 2 k 4 Invariant distribution of full system given by � � k 4 , λ 2 = k 1 ( k 3 + k 4 ) λ 1 = k 1 P k 2 k 4 � � k 1 ( k 2 + k 3 + k 4 ) S ( ∞ ) ∼ P (True invariant distribution) k 2 k 4 QSSA error in Poisson intensity k 1 k 2 Simon Cotter Product form stationary dist. 9 / 35

  2. QSSA: Simple Example k 2 k 4 / ( k 2 + k 3 ) s k 1 ∅ − − − − → S − − − − − − − − − → ∅ Quantify error by computing error in invariant distribution of S = X 1 + X 2 � k 1 ( k 2 + k 3 ) � S ( ∞ ) ∼ P (QSSA approximation) k 2 k 4 Invariant distribution of full system given by � � k 4 , λ 2 = k 1 ( k 3 + k 4 ) λ 1 = k 1 P k 2 k 4 � � k 1 ( k 2 + k 3 + k 4 ) S ( ∞ ) ∼ P (True invariant distribution) k 2 k 4 QSSA error in Poisson intensity k 1 k 2 Simon Cotter Product form stationary dist. 9 / 35

  3. QSSA: Simple Example k 2 k 4 / ( k 2 + k 3 ) s k 1 ∅ − − − − → S − − − − − − − − − → ∅ Quantify error by computing error in invariant distribution of S = X 1 + X 2 � k 1 ( k 2 + k 3 ) � S ( ∞ ) ∼ P (QSSA approximation) k 2 k 4 Invariant distribution of full system given by � � k 4 , λ 2 = k 1 ( k 3 + k 4 ) λ 1 = k 1 P k 2 k 4 � � k 1 ( k 2 + k 3 + k 4 ) S ( ∞ ) ∼ P (True invariant distribution) k 2 k 4 QSSA error in Poisson intensity k 1 k 2 Simon Cotter Product form stationary dist. 9 / 35

  4. Outline Introduction 1 The Quasi Steady-State Assumption 2 The Constrained Approach 3 Product Form Stationary Distributions for Non-Mass Action 4 Kinetics 5 Numerical Example Conclusions 6 Simon Cotter Product form stationary dist. 9 / 35

  5. The Constrained Approach The Constrained philosophy The assumption is that the fast variables equilibrate on a timescale which is negligible with respect to the rate of change of slow species, but that the invariant distribution of the fast variables can be affected by the slow reactions . Slow stoichiometries are not in general perpendicular to the fast stoichiometries! In practice We cannot approximate P ( F | S ) by considering just the fast subsystem, as we need to take into account the effect of the slow reactions on the invariant distribution of the fast variables . This can be approximated by considering the dynamics of the full system, constrained to a particular value of the slow variables . NB: Assymptotically (in the limit of large timescale gaps), this approach is in agreement with the QSSA Simon Cotter Product form stationary dist. 10 / 35

  6. The Constrained Approach The Constrained philosophy The assumption is that the fast variables equilibrate on a timescale which is negligible with respect to the rate of change of slow species, but that the invariant distribution of the fast variables can be affected by the slow reactions . Slow stoichiometries are not in general perpendicular to the fast stoichiometries! In practice We cannot approximate P ( F | S ) by considering just the fast subsystem, as we need to take into account the effect of the slow reactions on the invariant distribution of the fast variables . This can be approximated by considering the dynamics of the full system, constrained to a particular value of the slow variables . NB: Assymptotically (in the limit of large timescale gaps), this approach is in agreement with the QSSA Simon Cotter Product form stationary dist. 10 / 35

  7. The Constrained Approach The Constrained philosophy The assumption is that the fast variables equilibrate on a timescale which is negligible with respect to the rate of change of slow species, but that the invariant distribution of the fast variables can be affected by the slow reactions . Slow stoichiometries are not in general perpendicular to the fast stoichiometries! In practice We cannot approximate P ( F | S ) by considering just the fast subsystem, as we need to take into account the effect of the slow reactions on the invariant distribution of the fast variables . This can be approximated by considering the dynamics of the full system, constrained to a particular value of the slow variables . NB: Assymptotically (in the limit of large timescale gaps), this approach is in agreement with the QSSA Simon Cotter Product form stationary dist. 10 / 35

  8. The Constrained Approach ν ′ R 1 : ν 1 → 1 , ν ′ R 2 : ν 2 → 2 , . . . ν ′ R M : ν M → M , Pick slow variable S = � i a ij X i which is invariant with respect to fast reactions, i.e. perpendicular to fast stoichiometries Form basis with the slow variables, along with chosen fast variables F Define constrained stoichiometric projector P : R d → R d P ([ S , F ]) = [ 0 , F ] Simon Cotter Product form stationary dist. 11 / 35

  9. The Constrained Approach ν ′ R 1 : ν 1 → 1 , ν ′ R 2 : ν 2 → 2 , . . . ν ′ R M : ν M → M , Pick slow variable S = � i a ij X i which is invariant with respect to fast reactions, i.e. perpendicular to fast stoichiometries Form basis with the slow variables, along with chosen fast variables F Define constrained stoichiometric projector P : R d → R d P ([ S , F ]) = [ 0 , F ] Simon Cotter Product form stationary dist. 11 / 35

  10. The Constrained Approach ν ′ R 1 : ν 1 → 1 , ν ′ R 2 : ν 2 → 2 , . . . ν ′ R M : ν M → M , Pick slow variable S = � i a ij X i which is invariant with respect to fast reactions, i.e. perpendicular to fast stoichiometries Form basis with the slow variables, along with chosen fast variables F Define constrained stoichiometric projector P : R d → R d P ([ S , F ]) = [ 0 , F ] Simon Cotter Product form stationary dist. 11 / 35

  11. The Constrained Approach ν ′ R 1 : ν 1 → 1 , ν ′ R 2 : ν 2 → 2 , . . . ν ′ R M : ν M → M , Pick slow variable S = � i a ij X i which is invariant with respect to fast reactions, i.e. perpendicular to fast stoichiometries Form basis with the slow variables, along with chosen fast variables F Define constrained stoichiometric projector P : R d → R d P ([ S , F ]) = [ 0 , F ] Simon Cotter Product form stationary dist. 11 / 35

  12. The Constrained Subsystem ν 1 + P ( ν ′ R 1 : ν 1 → 1 − ν 1 ) = ˆ ν 1 , ν 2 + P ( ν ′ → 2 − ν 2 ) = ˆ R 2 : ν 2 ν 2 , . . . ν M + P ( ν ′ R M : ν M → M − ν M ) = ˆ ν M . Preserves changes to fast variables, removes changes to slow variables Multiply propensities by ✶ X + P ( ν ′ 0 to preserve k − ν k ) ∈ Z d non-negativity Constrains the slow variable to its starting value Invariant distribution a good approximation of P ( F | S ) for full system Invariant distribution of constrained system needs to be found Simon Cotter Product form stationary dist. 12 / 35

  13. The Constrained Subsystem ν 1 + P ( ν ′ R 1 : ν 1 → 1 − ν 1 ) = ˆ ν 1 , ν 2 + P ( ν ′ → 2 − ν 2 ) = ˆ R 2 : ν 2 ν 2 , . . . ν M + P ( ν ′ R M : ν M → M − ν M ) = ˆ ν M . Preserves changes to fast variables, removes changes to slow variables Multiply propensities by ✶ X + P ( ν ′ 0 to preserve k − ν k ) ∈ Z d non-negativity Constrains the slow variable to its starting value Invariant distribution a good approximation of P ( F | S ) for full system Invariant distribution of constrained system needs to be found Simon Cotter Product form stationary dist. 12 / 35

  14. The Constrained Subsystem ν 1 + P ( ν ′ R 1 : ν 1 → 1 − ν 1 ) = ˆ ν 1 , ν 2 + P ( ν ′ → 2 − ν 2 ) = ˆ R 2 : ν 2 ν 2 , . . . ν M + P ( ν ′ R M : ν M → M − ν M ) = ˆ ν M . Preserves changes to fast variables, removes changes to slow variables Multiply propensities by ✶ X + P ( ν ′ 0 to preserve k − ν k ) ∈ Z d non-negativity Constrains the slow variable to its starting value Invariant distribution a good approximation of P ( F | S ) for full system Invariant distribution of constrained system needs to be found Simon Cotter Product form stationary dist. 12 / 35

  15. The Constrained Subsystem ν 1 + P ( ν ′ R 1 : ν 1 → 1 − ν 1 ) = ˆ ν 1 , ν 2 + P ( ν ′ → 2 − ν 2 ) = ˆ R 2 : ν 2 ν 2 , . . . ν M + P ( ν ′ R M : ν M → M − ν M ) = ˆ ν M . Preserves changes to fast variables, removes changes to slow variables Multiply propensities by ✶ X + P ( ν ′ 0 to preserve k − ν k ) ∈ Z d non-negativity Constrains the slow variable to its starting value Invariant distribution a good approximation of P ( F | S ) for full system Invariant distribution of constrained system needs to be found Simon Cotter Product form stationary dist. 12 / 35

  16. The Constrained Subsystem ν 1 + P ( ν ′ R 1 : ν 1 → 1 − ν 1 ) = ˆ ν 1 , ν 2 + P ( ν ′ → 2 − ν 2 ) = ˆ R 2 : ν 2 ν 2 , . . . ν M + P ( ν ′ R M : ν M → M − ν M ) = ˆ ν M . Preserves changes to fast variables, removes changes to slow variables Multiply propensities by ✶ X + P ( ν ′ 0 to preserve k − ν k ) ∈ Z d non-negativity Constrains the slow variable to its starting value Invariant distribution a good approximation of P ( F | S ) for full system Invariant distribution of constrained system needs to be found Simon Cotter Product form stationary dist. 12 / 35

  17. The Constrained Subsystem ν 1 + P ( ν ′ R 1 : ν 1 → 1 − ν 1 ) = ˆ ν 1 , ν 2 + P ( ν ′ → 2 − ν 2 ) = ˆ R 2 : ν 2 ν 2 , . . . ν M + P ( ν ′ R M : ν M → M − ν M ) = ˆ ν M . Preserves changes to fast variables, removes changes to slow variables Multiply propensities by ✶ X + P ( ν ′ 0 to preserve k − ν k ) ∈ Z d non-negativity Constrains the slow variable to its starting value Invariant distribution a good approximation of P ( F | S ) for full system Invariant distribution of constrained system needs to be found Simon Cotter Product form stationary dist. 12 / 35

  18. Constrained Approach: Simple Example Consider the system: k 2 x 1 − − − − → k 1 k 4 x 2 → X 1 X 2 ∅ − − − − ← − − − − − − − − → ∅ k 3 x 2 First construct basis made up of slow/fast variables S = X 1 + X 2 , F = X 1 or F = X 2 We will pick F = X 2 Therefore P ([ X 1 , X 2 ]) = [ − X 2 , X 2 ] Apply to all reactions to arrive at constrained subsystem Simon Cotter Product form stationary dist. 13 / 35

  19. Constrained Approach: Simple Example Consider the system: k 2 x 1 − − − − → k 1 k 4 x 2 → X 1 X 2 ∅ − − − − ← − − − − − − − − → ∅ k 3 x 2 First construct basis made up of slow/fast variables S = X 1 + X 2 , F = X 1 or F = X 2 We will pick F = X 2 Therefore P ([ X 1 , X 2 ]) = [ − X 2 , X 2 ] Apply to all reactions to arrive at constrained subsystem Simon Cotter Product form stationary dist. 13 / 35

  20. Constrained Approach: Simple Example Consider the system: k 2 x 1 − − − − → k 1 k 4 x 2 → X 1 X 2 ∅ − − − − ← − − − − − − − − → ∅ k 3 x 2 First construct basis made up of slow/fast variables S = X 1 + X 2 , F = X 1 or F = X 2 We will pick F = X 2 Therefore P ([ X 1 , X 2 ]) = [ − X 2 , X 2 ] Apply to all reactions to arrive at constrained subsystem Simon Cotter Product form stationary dist. 13 / 35

  21. Constrained Approach: Simple Example Consider the system: k 2 x 1 − − − − → k 1 k 4 x 2 → X 1 X 2 ∅ − − − − ← − − − − − − − − → ∅ k 3 x 2 First construct basis made up of slow/fast variables S = X 1 + X 2 , F = X 1 or F = X 2 We will pick F = X 2 Therefore P ([ X 1 , X 2 ]) = [ − X 2 , X 2 ] Apply to all reactions to arrive at constrained subsystem Simon Cotter Product form stationary dist. 13 / 35

  22. Constrained Approach: Simple Example Consider the system: k 2 x 1 − − − − → k 1 k 4 x 2 → X 1 X 2 ∅ − − − − ← − − − − − − − − → ∅ k 3 x 2 First construct basis made up of slow/fast variables S = X 1 + X 2 , F = X 1 or F = X 2 We will pick F = X 2 Therefore P ([ X 1 , X 2 ]) = [ − X 2 , X 2 ] Apply to all reactions to arrive at constrained subsystem Simon Cotter Product form stationary dist. 13 / 35

  23. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  24. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  25. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  26. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  27. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  28. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  29. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  30. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  31. Constrained Approach: Simple Example k 1 R 1 : ∅ − − − − → X 1 Reaction 1: P ([ 1 , 0 ]) = [ 0 , 0 ] Constrained version of R 1 has no effect on X k 2 x 1 − − − − → R 2 , R 3 : X 1 X 2 Reactions 2,3: ← − − − − k 3 x 2 No change in S Projection has no effect k 4 x 2 − − − − → ∅ Reaction 4: R 4 : X 2 P ([ 0 , − 1 ]) = [ 1 , − 1 ] k 4 x 2 − − − − − → X 1 Constrained version: R 4 : X 2 Simon Cotter Product form stationary dist. 14 / 35

  32. Constrained Approach: Simple Example k 2 x 1 − − − − − − − → X 1 X 2 , ← − − − − − − − S = X 1 + X 2 ( k 3 + k 4 ) x 2 Invariant distribution X 2 ∼ B ( S , λ 2 ) = π ( X 2 ) � � ( k 3 + k 4 ) k 2 [ λ 1 , λ 2 ] = k 2 + k 3 + k 4 , steady state solution of mean field k 2 + k 3 + k 4 ODE: k 2 λ 1 = ( k 3 + k 4 ) λ 2 , λ 1 + λ 2 = 1 Compute expectation of the rate of reaction R 4 k 2 k 4 S α 4 = E ( α 4 | S ) = k 4 E ( X 2 | S ) = ˆ k 2 + k 3 + k 4 Simon Cotter Product form stationary dist. 15 / 35

  33. Constrained Approach: Simple Example k 2 x 1 − − − − − − − → X 1 X 2 , ← − − − − − − − S = X 1 + X 2 ( k 3 + k 4 ) x 2 Invariant distribution X 2 ∼ B ( S , λ 2 ) = π ( X 2 ) � � ( k 3 + k 4 ) k 2 [ λ 1 , λ 2 ] = k 2 + k 3 + k 4 , steady state solution of mean field k 2 + k 3 + k 4 ODE: k 2 λ 1 = ( k 3 + k 4 ) λ 2 , λ 1 + λ 2 = 1 Compute expectation of the rate of reaction R 4 k 2 k 4 S α 4 = E ( α 4 | S ) = k 4 E ( X 2 | S ) = ˆ k 2 + k 3 + k 4 Simon Cotter Product form stationary dist. 15 / 35

  34. Constrained Approach: Simple Example k 2 x 1 − − − − − − − → X 1 X 2 , ← − − − − − − − S = X 1 + X 2 ( k 3 + k 4 ) x 2 Invariant distribution X 2 ∼ B ( S , λ 2 ) = π ( X 2 ) � � ( k 3 + k 4 ) k 2 [ λ 1 , λ 2 ] = k 2 + k 3 + k 4 , steady state solution of mean field k 2 + k 3 + k 4 ODE: k 2 λ 1 = ( k 3 + k 4 ) λ 2 , λ 1 + λ 2 = 1 Compute expectation of the rate of reaction R 4 k 2 k 4 S α 4 = E ( α 4 | S ) = k 4 E ( X 2 | S ) = ˆ k 2 + k 3 + k 4 Simon Cotter Product form stationary dist. 15 / 35

  35. Constrained Approach: Simple Example k 2 k 4 / ( k 2 + k 3 + k 4 ) s k 1 ∅ − − − − → S − − − − − − − − − − − → ∅ To compare with QSSA, compute invariant distribution � k 1 ( k 2 + k 3 + k 4 ) � S ( ∞ ) ∼ P (Constrained approximation) k 2 k 4 Invariant distribution identical to true invariant distribution of S = X 1 + X 2 Simon Cotter Product form stationary dist. 16 / 35

  36. Constrained Approach: Simple Example k 2 k 4 / ( k 2 + k 3 + k 4 ) s k 1 ∅ − − − − → S − − − − − − − − − − − → ∅ To compare with QSSA, compute invariant distribution � k 1 ( k 2 + k 3 + k 4 ) � S ( ∞ ) ∼ P (Constrained approximation) k 2 k 4 Invariant distribution identical to true invariant distribution of S = X 1 + X 2 Simon Cotter Product form stationary dist. 16 / 35

  37. Constrained Approach: Simple Example k 2 k 4 / ( k 2 + k 3 + k 4 ) s k 1 ∅ − − − − → S − − − − − − − − − − − → ∅ To compare with QSSA, compute invariant distribution � k 1 ( k 2 + k 3 + k 4 ) � S ( ∞ ) ∼ P (Constrained approximation) k 2 k 4 Invariant distribution identical to true invariant distribution of S = X 1 + X 2 Simon Cotter Product form stationary dist. 16 / 35

  38. Simple Example 0.07 Full generator QSSA generator 0.06 CMA generator 0.05 Probability Mass 0.04 0.03 0.02 0.01 0 0 20 40 60 80 100 S = X 1 + X 2 SLC, “Constrained Approximation of Effective Generators for Multiscale Stochastic Reaction Networks and Application to Conditioned Path Sampling”, in review. Simon Cotter Product form stationary dist. 17 / 35

  39. Outline Introduction 1 The Quasi Steady-State Assumption 2 The Constrained Approach 3 Product Form Stationary Distributions for Non-Mass Action 4 Kinetics 5 Numerical Example Conclusions 6 Simon Cotter Product form stationary dist. 17 / 35

  40. Some Network Properties: Complexes k − → S 3 S 1 + S 2 S 1 + S 2 reactant complex S 3 product complex C number of complexes in network k 1 X 1 ( X 1 − 1 ) − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 C = 4 Simon Cotter Product form stationary dist. 18 / 35

  41. Some Network Properties: Complexes k − → S 3 S 1 + S 2 S 1 + S 2 reactant complex S 3 product complex C number of complexes in network k 1 X 1 ( X 1 − 1 ) − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 C = 4 Simon Cotter Product form stationary dist. 18 / 35

  42. Some Network Properties: Complexes k − → S 3 S 1 + S 2 S 1 + S 2 reactant complex S 3 product complex C number of complexes in network k 1 X 1 ( X 1 − 1 ) − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 C = 4 Simon Cotter Product form stationary dist. 18 / 35

  43. Some Network Properties: Complexes k − → S 3 S 1 + S 2 S 1 + S 2 reactant complex S 3 product complex C number of complexes in network k 1 X 1 ( X 1 − 1 ) − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 C = 4 Simon Cotter Product form stationary dist. 18 / 35

  44. Some Network Properties: Complexes k − → S 3 S 1 + S 2 S 1 + S 2 reactant complex S 3 product complex C number of complexes in network k 1 X 1 ( X 1 − 1 ) − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 C = 4 Simon Cotter Product form stationary dist. 18 / 35

  45. Some Network Properties: Complexes k − → S 3 S 1 + S 2 S 1 + S 2 reactant complex S 3 product complex C number of complexes in network k 1 X 1 ( X 1 − 1 ) − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 C = 4 Simon Cotter Product form stationary dist. 18 / 35

  46. Some Network Properties: Linkage Classes Network can be represented uniquely by graph with C nodes k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 2 S 1 S 2 S 1 ∅ Each connected graph is a linkage class l number of linkage classes (in this example l = 1) Simon Cotter Product form stationary dist. 19 / 35

  47. Some Network Properties: Linkage Classes Network can be represented uniquely by graph with C nodes k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 2 S 1 S 2 S 1 ∅ Each connected graph is a linkage class l number of linkage classes (in this example l = 1) Simon Cotter Product form stationary dist. 19 / 35

  48. Some Network Properties: Linkage Classes Network can be represented uniquely by graph with C nodes k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 2 S 1 S 2 S 1 ∅ Each connected graph is a linkage class l number of linkage classes (in this example l = 1) Simon Cotter Product form stationary dist. 19 / 35

  49. Some Network Properties: Linkage Classes Network can be represented uniquely by graph with C nodes k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 2 S 1 S 2 S 1 ∅ Each connected graph is a linkage class l number of linkage classes (in this example l = 1) Simon Cotter Product form stationary dist. 19 / 35

  50. Some Network Properties: Linkage Classes Network can be represented uniquely by graph with C nodes k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 2 S 1 S 2 S 1 ∅ Each connected graph is a linkage class l number of linkage classes (in this example l = 1) Simon Cotter Product form stationary dist. 19 / 35

  51. Some Network Properties: Stoichiometric Subspace Denote each reaction as: → ν ′ ν m − − − − m Stochiometric subspace given by: S = span m { ν m − ν ′ m } Denote s = dim ( S ) Simon Cotter Product form stationary dist. 20 / 35

  52. Some Network Properties: Stoichiometric Subspace Denote each reaction as: → ν ′ ν m − − − − m Stochiometric subspace given by: S = span m { ν m − ν ′ m } Denote s = dim ( S ) Simon Cotter Product form stationary dist. 20 / 35

  53. Some Network Properties: Stoichiometric Subspace Denote each reaction as: → ν ′ ν m − − − − m Stochiometric subspace given by: S = span m { ν m − ν ′ m } Denote s = dim ( S ) Simon Cotter Product form stationary dist. 20 / 35

  54. Some Network Properties: Deficiency Zero Deficiency δ = C − l − s k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , − − − − → ∅ , S 1 k 2 X 2 δ = 4 − 1 − 2 = 1 Networks with deficiency zero have certain properties and are well studied Simon Cotter Product form stationary dist. 21 / 35

  55. Some Network Properties: Deficiency Zero Deficiency δ = C − l − s k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , − − − − → ∅ , S 1 k 2 X 2 δ = 4 − 1 − 2 = 1 Networks with deficiency zero have certain properties and are well studied Simon Cotter Product form stationary dist. 21 / 35

  56. Some Network Properties: Deficiency Zero Deficiency δ = C − l − s k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , − − − − → ∅ , S 1 k 2 X 2 δ = 4 − 1 − 2 = 1 Networks with deficiency zero have certain properties and are well studied Simon Cotter Product form stationary dist. 21 / 35

  57. Some Network Properties: Weak Reversibility ODE models of zero deficiency weakly reversible networks have a unique complex balance (steady-state of the ODE) System is reversible if all reactions are reversible 1 2 3 C 1 C 2 C 3 5 4 C 5 C 4 Simon Cotter Product form stationary dist. 22 / 35

  58. Some Network Properties: Weak Reversibility ODE models of zero deficiency weakly reversible networks have a unique complex balance (steady-state of the ODE) System is reversible if all reactions are reversible 1 2 3 C 1 C 2 C 3 5 4 C 5 C 4 Simon Cotter Product form stationary dist. 22 / 35

  59. Some Network Properties: Weak Reversibility ODE models of zero deficiency weakly reversible networks have a unique complex balance (steady-state of the ODE) System is reversible if all reactions are reversible 1 2 3 C 1 C 2 C 3 5 4 C 5 C 4 Simon Cotter Product form stationary dist. 22 / 35

  60. Some Network Properties: Weak Reversibility ODE models of zero deficiency weakly reversible networks have a unique complex balance (steady-state of the ODE) System is reversible if all reactions are reversible 1 2 3 C 1 C 2 C 3 5 4 C 5 C 4 Simon Cotter Product form stationary dist. 22 / 35

  61. Some Network Properties: Weak Reversibility ODE models of zero deficiency weakly reversible networks have a unique complex balance (steady-state of the ODE) System is reversible if all reactions are reversible 1 2 3 C 1 C 2 C 3 5 4 C 5 C 4 Simon Cotter Product form stationary dist. 22 / 35

  62. Some Network Properties: Weak Reversibility ODE models of zero deficiency weakly reversible networks have a unique complex balance (steady-state of the ODE) System is reversible if all reactions are reversible 1 2 3 C 1 C 2 C 3 5 4 C 5 C 4 Simon Cotter Product form stationary dist. 22 / 35

  63. Some Network Properties: Weak Reversibility ODE models of zero deficiency weakly reversible networks have a unique complex balance (steady-state of the ODE) System is reversible if all reactions are reversible 1 2 3 C 1 C 2 C 3 5 4 C 5 C 4 Simon Cotter Product form stationary dist. 22 / 35

  64. Preliminaries: form of intensity functions The theorem that follows relies on the following form of the intensity/hazard functions d ν mi − 1 � � α m ( x ) = k m θ i ( x i − j ) , i = 1 j = 0 Mass action kinetics if θ is the identity Simon Cotter Product form stationary dist. 23 / 35

  65. Preliminaries: form of intensity functions The theorem that follows relies on the following form of the intensity/hazard functions d ν mi − 1 � � α m ( x ) = k m θ i ( x i − j ) , i = 1 j = 0 Mass action kinetics if θ is the identity Simon Cotter Product form stationary dist. 23 / 35

  66. Preliminaries: form of intensity functions The theorem that follows relies on the following form of the intensity/hazard functions d ν mi − 1 � � α m ( x ) = k m θ i ( x i − j ) , i = 1 j = 0 Mass action kinetics if θ is the identity Simon Cotter Product form stationary dist. 23 / 35

  67. Product Form Stationary Distributions Theorem (Anderson, Craciun, Kurtz, 2010) Let {S , C , R} be a zero deficiency, weakly reversible reaction network. Modeled deterministically with mass action kinetics and rate constants k m the system has complex balanced equilibrium c ∈ R d > 0 . Then, the stochastically modeled system with the specified intensity functions admits the invariant measure on each stoichiometric class d c x i � i π ( x ) ∝ . � x i − 1 j = 0 θ i ( x i − j ) i = 1 The measure π can be normalized to a stationary distribution so long as it is summable. Simon Cotter Product form stationary dist. 24 / 35

  68. Motivating Example for New Result k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 Multiscale system with reversible dimerisation reactions fast Consider the constrained fast subsystem with slow variable S = X 1 + 2 X 2 k 1 X 1 ( X 1 − 1 )+ k 3 ✶ { X 1 > 1 } − − − − − − − − − − − → 2 S 1 S 2 , ← − − − − − − − − − − − ( k 2 + k 4 ) X 2 Intensity functions do not satisfy the assumptions of the existing results Simon Cotter Product form stationary dist. 25 / 35

  69. Motivating Example for New Result k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 Multiscale system with reversible dimerisation reactions fast Consider the constrained fast subsystem with slow variable S = X 1 + 2 X 2 k 1 X 1 ( X 1 − 1 )+ k 3 ✶ { X 1 > 1 } − − − − − − − − − − − → 2 S 1 S 2 , ← − − − − − − − − − − − ( k 2 + k 4 ) X 2 Intensity functions do not satisfy the assumptions of the existing results Simon Cotter Product form stationary dist. 25 / 35

  70. Motivating Example for New Result k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 Multiscale system with reversible dimerisation reactions fast Consider the constrained fast subsystem with slow variable S = X 1 + 2 X 2 k 1 X 1 ( X 1 − 1 )+ k 3 ✶ { X 1 > 1 } − − − − − − − − − − − → 2 S 1 S 2 , ← − − − − − − − − − − − ( k 2 + k 4 ) X 2 Intensity functions do not satisfy the assumptions of the existing results Simon Cotter Product form stationary dist. 25 / 35

  71. Motivating Example for New Result k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 Multiscale system with reversible dimerisation reactions fast Consider the constrained fast subsystem with slow variable S = X 1 + 2 X 2 k 1 X 1 ( X 1 − 1 )+ k 3 ✶ { X 1 > 1 } − − − − − − − − − − − → 2 S 1 S 2 , ← − − − − − − − − − − − ( k 2 + k 4 ) X 2 Intensity functions do not satisfy the assumptions of the existing results Simon Cotter Product form stationary dist. 25 / 35

  72. Motivating Example for New Result k 1 X 1 ( X 1 − 1 ) − − − − − − − → k 3 k 4 X 1 2 S 1 S 2 , ← − − − − − − − ∅ − − − − → S 2 , S 1 − − − − → ∅ , k 2 X 2 Multiscale system with reversible dimerisation reactions fast Consider the constrained fast subsystem with slow variable S = X 1 + 2 X 2 k 1 X 1 ( X 1 − 1 )+ k 3 ✶ { X 1 > 1 } − − − − − − − − − − − → 2 S 1 S 2 , ← − − − − − − − − − − − ( k 2 + k 4 ) X 2 Intensity functions do not satisfy the assumptions of the existing results Simon Cotter Product form stationary dist. 25 / 35

  73. New Structural Assumption Partition all species S = { S 1 , S 2 , . . . , S N } into S 1 and S 2 . S i ∈ S 2 if for some η i ≥ 2 we have that ν ki is always some nonnegative multiple of η i For all other S i ∈ S 1 , let η i = 1. Assume that all intensity functions satisfy: ν mi η i − 1 d � � α m ( x ) = k m θ i ( X i − j η i ) , i = 1 j = 0 where κ k > 0 and θ i ( x i ) = 0 if and only if x i ≤ α i − 1. Simon Cotter Product form stationary dist. 26 / 35

  74. New Structural Assumption Partition all species S = { S 1 , S 2 , . . . , S N } into S 1 and S 2 . S i ∈ S 2 if for some η i ≥ 2 we have that ν ki is always some nonnegative multiple of η i For all other S i ∈ S 1 , let η i = 1. Assume that all intensity functions satisfy: ν mi η i − 1 d � � α m ( x ) = k m θ i ( X i − j η i ) , i = 1 j = 0 where κ k > 0 and θ i ( x i ) = 0 if and only if x i ≤ α i − 1. Simon Cotter Product form stationary dist. 26 / 35

  75. New Structural Assumption Partition all species S = { S 1 , S 2 , . . . , S N } into S 1 and S 2 . S i ∈ S 2 if for some η i ≥ 2 we have that ν ki is always some nonnegative multiple of η i For all other S i ∈ S 1 , let η i = 1. Assume that all intensity functions satisfy: ν mi η i − 1 d � � α m ( x ) = k m θ i ( X i − j η i ) , i = 1 j = 0 where κ k > 0 and θ i ( x i ) = 0 if and only if x i ≤ α i − 1. Simon Cotter Product form stationary dist. 26 / 35

  76. New Structural Assumption Partition all species S = { S 1 , S 2 , . . . , S N } into S 1 and S 2 . S i ∈ S 2 if for some η i ≥ 2 we have that ν ki is always some nonnegative multiple of η i For all other S i ∈ S 1 , let η i = 1. Assume that all intensity functions satisfy: ν mi η i − 1 d � � α m ( x ) = k m θ i ( X i − j η i ) , i = 1 j = 0 where κ k > 0 and θ i ( x i ) = 0 if and only if x i ≤ α i − 1. Simon Cotter Product form stationary dist. 26 / 35

  77. New Structural Assumption Partition all species S = { S 1 , S 2 , . . . , S N } into S 1 and S 2 . S i ∈ S 2 if for some η i ≥ 2 we have that ν ki is always some nonnegative multiple of η i For all other S i ∈ S 1 , let η i = 1. Assume that all intensity functions satisfy: ν mi η i − 1 d � � α m ( x ) = k m θ i ( X i − j η i ) , i = 1 j = 0 where κ k > 0 and θ i ( x i ) = 0 if and only if x i ≤ α i − 1. Simon Cotter Product form stationary dist. 26 / 35

  78. Theorem: Product Form Stationary Distributions Theorem (Anderson, Cotter, 2016) Let {S 1 ∪ S 2 , C , R} be a zero deficiency, weakly reversible reaction network satisfying the above assumption. Modeled deterministically with mass action kinetics and rate constants k m the system has complex balanced equilibrium c ∈ R d > 0 . Then, the stochastically modeled system with the specified intensity functions admits the invariant measure on each stoichiometric class d c X i � i π ( x ) ∝ . � ⌊ X i /η i ⌋− 1 θ i ( X i − j η i ) i = 1 j = 0 The measure π can be normalized to a stationary distribution so long as it is summable. Simon Cotter Product form stationary dist. 27 / 35

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