Added MC-VQE ground state calculation test.

Signed-off-by: Dmitry I. Lyakh <quant4me@gmail.com>

src/exatn/tests/NumServerTester.cpp

@@ -16,7 +16,7 @@
 #include "errors.hpp"
 
 //Test activation:
-#define EXATN_TEST0
+/*#define EXATN_TEST0
 #define EXATN_TEST1
 #define EXATN_TEST2
 #define EXATN_TEST3
@@ -41,10 +41,10 @@
 #define EXATN_TEST22
 #define EXATN_TEST23
 #define EXATN_TEST24
-#define EXATN_TEST25
+#define EXATN_TEST25*/
 #define EXATN_TEST26 //requires input file from source
-#define EXATN_TEST27
-#define EXATN_TEST28
+//#define EXATN_TEST27
+//#define EXATN_TEST28
 
 
 #ifdef EXATN_TEST0
@@ -2825,7 +2825,9 @@ TEST(NumServerTester, HubbardHamiltonian) {
  const int num_sites = 8, max_bond_dim = std::min(static_cast<int>(std::pow(2,num_sites/2)),16); //2x2 sites x dim(4) = 8 qubits (sites)
 
  //Read 2x2 Hubbard Hamiltonian in spin representation:
- auto hubbard_operator = exatn::quantum::readSpinHamiltonian("HubbardHam","hubbard_2x2.txt",TENS_ELEM_TYPE);
+ //auto hubbard_operator = exatn::quantum::readSpinHamiltonian("MCVQEHam","mcvqe_8q.txt",TENS_ELEM_TYPE);
+ //success = hubbard_operator->deleteComponent(0); assert(success);
+ auto hubbard_operator = exatn::quantum::readSpinHamiltonian("HubbardHam","hubbard_2x2_8q.txt",TENS_ELEM_TYPE);
  hubbard_operator->printIt();
 
  //Create tensor network ansatz:

src/exatn/tests/mcvqe_8q.txt

+(-10729.963236109992+0j) [] +
+(0.013958292661992958+0j) [X0] +
+(0.017780394781136848+0j) [X0 X1] +
+(-0.006896704529177866+0j) [X0 Z1] +
+(-0.03376113630025557+0j) [Z0] +
+(0.011474775121306156+0j) [Z0 X1] +
+(-0.004444563032874407+0j) [Z0 Z1] +
+(0.009522097764876093+0j) [X1] +
+(-0.008640686174448204+0j) [X1 X2] +
+(-0.00641012019143096+0j) [X1 Z2] +
+(-0.042308599255825224+0j) [Z1] +
+(0.0033005482717231548+0j) [Z1 X2] +
+(0.0024514303165071353+0j) [Z1 Z2] +
+(-0.006583545256676178+0j) [X2] +
+(-0.007287160094179741+0j) [X2 X3] +
+(0.004086379532445629+0j) [X2 Z3] +
+(-0.04957343856301523+0j) [Z2] +
+(-0.005120355594249221+0j) [Z2 X3] +
+(0.00289351687114843+0j) [Z2 Z3] +
+(-0.006327031384126287+0j) [X3] +
+(-0.01840086316143409+0j) [X3 X4] +
+(-0.012367083572855955+0j) [X3 Z4] +
+(-0.03839552410604509+0j) [Z3] +
+(0.010913763352627169+0j) [Z3 X4] +
+(0.007334390217786867+0j) [Z3 Z4] +
+(0.009699304994889446+0j) [X4] +
+(-0.004742884975867185+0j) [X4 X5] +
+(-0.0011410992924187104+0j) [X4 Z5] +
+(-0.03672437524536075+0j) [Z4] +
+(-0.0028540627220499703+0j) [Z4 X5] +
+(-0.0006758931704842083+0j) [Z4 Z5] +
+(-0.008546718038275256+0j) [X5] +
+(0.0012774322501627943+0j) [X5 X6] +
+(-0.0006862884757300228+0j) [X5 Z6] +
+(-0.040029787841621825+0j) [Z5] +
+(0.0004181198916071052+0j) [Z5 X6] +
+(-0.0002418324220780885+0j) [Z5 Z6] +
+(-0.004220761908087866+0j) [X6] +
+(-0.007850802949685699+0j) [X6 X7] +
+(-0.004536735382497114+0j) [X6 Z7] +
+(-0.041302161404488+0j) [Z6] +
+(0.005221816809904007+0j) [Z6 X7] +
+(0.003023554049679674+0j) [Z6 Z7] +
+(0.0023629329298370094+0j) [X7] +
+(-0.04139809785433139+0j) [Z7]

src/numerics/tensor_expansion.cpp

 /** ExaTN::Numerics: Tensor network expansion
-REVISION: 2021/08/09
+REVISION: 2021/09/20
 
 Copyright (C) 2018-2021 Dmitry I. Lyakh (Liakh)
 Copyright (C) 2018-2021 Oak Ridge National Laboratory (UT-Battelle) **/
@@ -205,6 +205,14 @@ bool TensorExpansion::appendExpansion(const TensorExpansion & another,
 }
 
 
+bool TensorExpansion::deleteComponent(std::size_t component_num)
+{
+ if(component_num >= components_.size()) return false;
+ components_.erase(components_.cbegin()+component_num);
+ return true;
+}
+
+
 void TensorExpansion::conjugate()
 {
  for(auto & component: components_){

src/numerics/tensor_expansion.hpp

 /** ExaTN::Numerics: Tensor network expansion
-REVISION: 2021/08/09
+REVISION: 2021/09/20
 
 Copyright (C) 2018-2021 Dmitry I. Lyakh (Liakh)
 Copyright (C) 2018-2021 Oak Ridge National Laboratory (UT-Battelle) **/
@@ -199,6 +199,9 @@ public:
  bool appendExpansion(const TensorExpansion & another,         //in: tensor network expansion
                       const std::complex<double> coefficient); //in: scaling coefficient (applies to the appended tensor network expansion)
 
+ /** Deletes the specified component of the tensor expansion. **/
+ bool deleteComponent(std::size_t component_num);
+
  /** Conjugates the tensor network expansion: All constituting tensors are complex conjugated,
      all tensor legs reverse their direction, complex linear expansion coefficients are conjugated:
      The ket tensor network expansion becomes a bra, and vice versa. **/

src/numerics/tensor_operator.cpp

 /** ExaTN::Numerics: Tensor operator
-REVISION: 2021/03/05
+REVISION: 2021/09/20
 
 Copyright (C) 2018-2021 Dmitry I. Lyakh (Liakh)
 Copyright (C) 2018-2021 Oak Ridge National Laboratory (UT-Battelle) **/
@@ -160,6 +160,14 @@ bool TensorOperator::appendSymmetrizeComponent(std::shared_ptr<Tensor> tensor,
 }
 
 
+bool TensorOperator::deleteComponent(std::size_t component_num)
+{
+ if(component_num >= components_.size()) return false;
+ components_.erase(components_.cbegin()+component_num);
+ return true;
+}
+
+
 void TensorOperator::conjugate()
 {
  for(auto & component: components_){

src/numerics/tensor_operator.hpp

 /** ExaTN::Numerics: Tensor operator
-REVISION: 2021/03/05
+REVISION: 2021/09/20
 
 Copyright (C) 2018-2021 Dmitry I. Lyakh (Liakh)
 Copyright (C) 2018-2021 Oak Ridge National Laboratory (UT-Battelle) **/
@@ -135,6 +135,9 @@ public:
                                 const std::complex<double> coefficient,        //in: expansion coefficient
                                 bool antisymmetrize = false);                  //in: whether or not to negate the coefficient for odd permutations
 
+ /** Deletes the specified component of the tensor operator. **/
+ bool deleteComponent(std::size_t component_num);
+
  /** Conjugates the tensor operator: All constituting tensors are complex conjugated,
      all tensor legs reverse their direction, bra legs and ket legs are swapped,
      complex linear expansion coefficients are complex conjugated. **/

src/numerics/tensor_symbol.cpp

@@ -378,10 +378,12 @@ bool parse_pauli_string(const std::string & input,
      const auto plus_pos = input.find("+",left_par_pos);
      if(plus_pos != std::string::npos){
       const auto real_len = plus_pos - left_par_pos - 1;
+      //std::cout << "#DEBUG(parse_pauli_string): Coef: " << input.substr(left_par_pos+1,real_len); //debug
       if(real_len > 0) coef_real = std::stod(input.substr(left_par_pos+1,real_len));
       const auto imag_end_pos = input.find("j",plus_pos);
       if(imag_end_pos != std::string::npos){
        const auto imag_len = imag_end_pos - plus_pos - 1;
+       //std::cout << " " << input.substr(plus_pos+1,imag_len) << std::endl; //debug
        if(imag_len > 0) coef_imag = std::stod(input.substr(plus_pos+1,imag_len));
        coefficient = std::complex<double>{coef_real, coef_imag};
       }else{