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PhD thesis in English

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2. Diagonalization of Transition Amplitudes10 2 0 0.5 1 1.5 2 2.5 3|| E 0(p) (∆, L, t) - E 0exact10 -2 110 -410 -610 -810 -1010 -12p = 1p = 2p = 4p = 6p = 8p = 10p = 12p = 1410 -2 1L10 -4| E 0(p) (∆, L, t) - E 0exact|10 -610 -810 -1810 -1210 -1410 -1610 -180.020.04t0.060.08p = 1p = 2p = 4p = 6p = 8p = 100.10.12Figure 2.13: Deviations from the ground energy |E (p)0 (∆, L, t) − E 0 | as a function ofthe space cutoff L (top) and as a function of the time t (bottom) for the potential(2.36) for k 2 = 0 and k 4 = 24. The discretization parameters are ∆ = 0.2, t = 0.1on the top graph, and L = 3 on the bottom graph. Deviations are calculated us<strong>in</strong>gthe ground energy E 0 = 1.47714975357799(4) obta<strong>in</strong>ed with p = 21 effective action.The dashed l<strong>in</strong>e <strong>in</strong> the bottom graph corresponds to the discretization error (2.19).usual saturation of errors for sufficiently large values of L. The saturated valuerapidly decreases (by several orders of magnitude) as we <strong>in</strong>crease the level p of theeffective action used to calculate space-discretized matrix of the evolution operator.Fig. 2.13(bottom) shows the time dependence of ground energy errors, which are48

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