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40 lines
999 B
40 lines
999 B
// herman's self stabilising algorithm [Her90]
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// gxn/dxp 13/07/02
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// the procotol is synchronous with no nondeterminism (a DTMC)
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dtmc
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const double p = 0.5;
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// module for process 1
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module process1
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// Boolean variable for process 1
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x1 : [0..1];
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[step] (x1=x3) -> p : (x1'=0) + 1-p : (x1'=1);
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[step] !(x1=x3) -> (x1'=x3);
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endmodule
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// add further processes through renaming
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module process2 = process1 [ x1=x2, x3=x1 ] endmodule
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module process3 = process1 [ x1=x3, x3=x2 ] endmodule
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// cost - 1 in each state (expected number of steps)
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rewards "steps"
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true : 1;
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endrewards
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// set of initial states: all (i.e. any possible initial configuration of tokens)
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init
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true
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endinit
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// formula, for use in properties: number of tokens
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// (i.e. number of processes that have the same value as the process to their left)
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formula num_tokens = (x1=x2?1:0)+(x2=x3?1:0)+(x3=x1?1:0);
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// label - stable configurations (1 token)
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label "stable" = num_tokens=1;
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