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NYC 9/11 Public Portal Document

132 Table 5.4 Computational Time on the CRAY-2 Supercomputer Using Various Starting Points (in Seconds)

Rents Rents Rents Rents Equil. Within Within Within Uniformly point J 10% 30% 50% Zero of Eq. of Eq. of Eq. (*) (*) (*)

Reading data and 112.83 113.21 112.97 112.85 113.17 initial comps. Housing equil. 3.19 9.58 22.10 315+ 316+ (itera­ (1) (3) (7) (99+) (99+) tions) Commercial equil. and 28.29 29.05 28.28 output computation

(*): Rents are randomized within the indicated band around the equilibrium point.Note : Above computations are based on the empirically based New York Model [463 employment 2ones(i=463);463 residence zones(j=463); 3 housing types (k=3);5 commuting modes(m=5);52 shopping zones(1=52);2 shopping modes(n=2)). The model’s housing market part has 847 equations and the commercial equilibrium part has 46 equations. The convergence tolerance is 0.5% of the equilibrium rents.

Tables 5.4 and 5.5 present the computational performance of the empirically based and vecterized NYREG solved on the NCSA CRAY-2. It is seen from these tables that one iteration in the housing market equilibrium part of the model takes slightly more than 3 seconds. The total time needed to complete all computations is at least 144.31 seconds and depends on how far the starting point of rents is from the equilibrium point of rents. When rents are randomly perturbed within 10% and 3 0% of the equilibrium point, then 3 to 7 iterations are needed to achieve convergence. Convergence is defined as the state when each rent is calculated to be within 0.5% of the corresponding equilibrium rent value.

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