Import ABACUS++G_8 code; cleanup files; new README

2018-02-09 17:34:05 +01:00
parent 61084ef3b3
commit 103cbe84d6
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+/**********************************************************
+
+This software is part of J.-S. Caux's ABACUS library.
+
+Copyright (c).
+
+-----------------------------------------------------------
+
+File:  LiebLin_Gaudin_lnnorm.cc
+
+Purpose:  calculates the Gaudin norm of a vector of arbitrary
+          complex rapidities 
+
+***********************************************************/
+
+#include "JSC.h"
+
+using namespace std;
+using namespace JSC;
+
+namespace JSC {
+
+  DP LiebLin_Twisted_lnnorm (Vect<complex<DP> >& lambdaoc, double cxL)
+  {
+    // Calculates the lnnorm of an eigenstate of the twisted transfer matrix
+    // so Gaudin can be used.
+
+    int N = lambdaoc.size();
+
+    SQMat<complex<DP> > Gaudin(N);
+
+    complex<DP> sum_Kernel = 0.0;
+
+    for (int j = 0; j < N; ++j) 
+      for (int k = 0; k < N; ++k) {
+	if (j == k) {
+	  sum_Kernel = 0.0;
+	  for (int kp = 0; kp < N; ++kp) if (j != kp) sum_Kernel += 2.0/((lambdaoc[j] - lambdaoc[kp]) * (lambdaoc[j] - lambdaoc[kp]) + 1.0);
+	  Gaudin[j][k] = cxL + sum_Kernel;
+	}
+	else Gaudin[j][k] = - 2.0/((lambdaoc[j] - lambdaoc[k]) * (lambdaoc[j] - lambdaoc[k]) + 1.0);
+      }
+
+    DP lnnorm = real(lndet_LU_CX_dstry(Gaudin));
+
+    // Add the pieces outside of Gaudin determinant
+    for (int j = 0; j < N - 1; ++j) for (int k = j+1; k < N; ++k) lnnorm += log(1.0 + 1.0/norm(lambdaoc[j] - lambdaoc[k]));
+
+    return(lnnorm);
+  }
+
+} // namespace JSC