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@@ -6,7 +6,7 @@ Copyright (c) J.-S. Caux
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-----------------------------------------------------------
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-File: ABACUS+_Usage_Example_Heis.cc
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+File: ABACUS_Usage_Example_Heis.cc
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Purpose: illustrates basic use of ABACUS for spin chains.
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@@ -22,20 +22,21 @@ int main()
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{
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clock_t StartTime = clock();
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- // Refer to include/JSC_Heis.h for all class definitions
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+ // Refer to include/ABACUS_Heis.h for all class definitions
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// and to src/HEIS/ for the actual implementations.
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// Set basic system parameters:
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DP Delta = 1.0; // anisotropy
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int N = 64; // chain length
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- int M = 32; // number of downturned spins as compared to all spins up; must be <= N/2 (on or above equator)
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+ int M = 32; // number of downturned spins; must be <= N/2 (on or above equator)
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// Define the chain: J, Delta, h, Nsites
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Heis_Chain chain(1.0, Delta, 0.0, N);
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// The Heis_Chain class so constructed contains information about all types of strings:
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cout << "Delta = " << Delta << endl << "Possible string lengths and parities: ";
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- for (int j = 0; j < chain.Nstrings; ++j) cout << "(" << chain.Str_L[j] << ", " << chain.par[j] << ")" << "\t";
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+ for (int j = 0; j < chain.Nstrings; ++j)
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+ cout << "(" << chain.Str_L[j] << ", " << chain.par[j] << ")" << "\t";
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cout << endl;
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@@ -64,22 +65,26 @@ int main()
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// Now define some excited state.
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// First method:
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- // Start with defining a base using a base constructor with a vector of numbers of rapidities of each type as argument:
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+ // Start with defining a base using a base constructor with a vector of
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+ // numbers of rapidities of each type as argument:
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// First define Nrapidities vector:
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Vect<int> Nrapidities(0, chain.Nstrings);
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- // Assigning the numbers that follow, you have to ensure (yourself!) the \sum_j M_j n_j = M (where n_j is the length of type j).
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+ // Assigning the numbers that follow, you have to ensure (yourself!) that
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+ // the \sum_j M_j n_j = M (where n_j is the length of type j).
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Nrapidities[0] = M-2; // number of one-strings
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Nrapidities[1] = 1; // one two-string
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// Define the base:
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Heis_Base ebase(chain, Nrapidities);
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// Once the base is defined, the limiting quantum numbers are automatically computed:
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cout << "ebase defined, data is (Mdown, Nrap, Nraptot, Ix2_infty, Ix2_min, Ix2_max, baselabel):"
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- << ebase.Mdown << endl << ebase.Nrap << endl << ebase.Nraptot << endl << ebase.Ix2_infty << endl
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+ << ebase.Mdown << endl << ebase.Nrap << endl << ebase.Nraptot << endl
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+ << ebase.Ix2_infty << endl
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<< ebase.Ix2_min << endl << ebase.Ix2_max << endl << ebase.baselabel << endl;
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// An excited state can then be defined using this new base:
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XXX_Bethe_State estate(chain, ebase);
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- // Individual quantum numbers can be manipulated: this will NOT update the state label or verify range of Ix2
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+ // Individual quantum numbers can be manipulated: this will NOT update the
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+ // state label or verify range of Ix2
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estate.Ix2[0][0] = M+1;
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estate.Compute_All(true);
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cout << endl << "estate: " << estate << endl;
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@@ -91,11 +96,12 @@ int main()
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// Construct a new Bethe state
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- XXX_Bethe_State estateref (chain, ebase2); // this will contain the lowest-energy quantum numbers for this base
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+ XXX_Bethe_State estateref (chain, ebase2); // defaults to the lowest-energy state for this base
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XXX_Bethe_State estate2 (chain, ebase2); // yet another state
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// Setting a state to a given label:
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- estate2.Set_to_Label ("31_1_nh", estateref.Ix2); // The base of estate must coincide with the base in the label. Label is relative to estateref.Ix2
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+ // The base of estate must coincide with the base in label. Label is relative to estateref.Ix2.
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+ estate2.Set_to_Label ("31_1_nh", estateref.Ix2);
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estate2.Compute_All(true);
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cout << "estate2: " << estate2 << endl;
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cout << "Excitation momentum (mod 2 pi) = estate.K - gstate.K = " << estate.K - gstate.K << endl;
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- // Computing matrix elements: CAREFUL: magnetizations must be consistent with operator (error is flagged).
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+ // Computing matrix elements:
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+ // CAREFUL: magnetizations must be consistent with operator (error is flagged).
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cout << "Matrix elements: " << endl;
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// The logarithm of the matrix elements are computed as complex numbers:
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cout << "ln_Sz (gstate, estate) = " << ln_Sz_ME (gstate, estate) << endl;
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J.-S. Caux
6 years ago