add QTensorCI contructor which takes a tensor train

include/xfac/tensor/tensor_ci_2.h

@@ -79,8 +79,8 @@ struct TensorCI2 {
     {}
 
     /// constructs a TensorCI2 from a given tensor train, and using the provided function f.
-    TensorCI2(function<T(vector<int>)> f_, TensorTrain<T> tt_, TensorCI2Param param_={})
-        : f {f_, param_.useCachedFunction}
+    TensorCI2(TensorFunction<T> const& f_, TensorTrain<T> tt_, TensorCI2Param param_={})
+        : f {f_}
         , param(param_)
         , pivotError(1)
         , Iset {tt_.M.size()}
@@ -124,6 +124,11 @@ struct TensorCI2 {
         iterate(1,0); // just to define tt, while reevaluating the original f in the pivots.
     }
 
+    /// constructs a TensorCI2 from a given tensor train, and using the provided function f.
+    TensorCI2(function<T(vector<int>)> f_, TensorTrain<T> tt_, TensorCI2Param param_={})
+        : TensorCI2(TensorFunction<T> {f_, param_.useCachedFunction}, tt_, param_)
+    {}
+
     /// constructs a TensorCI2 from a given tensor train. It takes the tt as a true function f.
     TensorCI2(TensorTrain<T> const& tt_, TensorCI2Param param_={}) : TensorCI2(tt_, tt_, param_) {}
 
@@ -399,6 +404,12 @@ class QTensorCI: public TensorCI2<T> {
         , grid {grid_}
     {}
 
+    /// constructs a QTensorCI from a function f:(u1,u2,...,un)->T, a tensor train and the given quantics grid
+    QTensorCI(function<T(vector<double>)> f_, grid::Quantics grid_, TensorTrain<T> tt_, TensorCI2Param par={})
+        : TensorCI2<T> {tensorFun(f_,grid_), tt_, par}
+        , grid {grid_}
+    {}
+
     /// returns the underline quantics tensor train
     QTensorTrain<T> get_qtt() const { return {this->tt, grid}; }
 

test/test_tensor_ci_2.cpp

@@ -143,6 +143,40 @@ TEST_CASE("quantics 2")
         cout << "true error=" << ci.trueError(1<<ci.grid.nBit) << "\n";
     }
 
+    SECTION( "restart from tensor train" )
+    {
+        function f2=[&](double x) { return pow(x+0.1,5)+pow(x-0.5,4); };
+        auto exact = pow(1.1,6)/6-pow(0.1,6)/6 + pow(0.5,5)/5+pow(0.5,5)/5;
+
+        map<double,double> cache;
+        auto f=[&](vector<double> y) { double x = y[0]; return cache[x]=f2(x); };
+
+        auto ci=QTensorCI<double>(f, grid::Quantics {0.0, 1.0, 30}, {.bondDim=20, .useCachedFunction=true});
+        ci.iterate(3);
+
+        auto ci_2=QTensorCI<double>(f, grid::Quantics {0.0, 1.0, 30}, ci.get_qtt().tt, {.bondDim=20, .useCachedFunction=true});
+        //ci_2.iterate();
+        auto res = ci_2.get_qtt().integral();
+        REQUIRE(std::abs(res - exact)<1e-9);
+    }
+
+    SECTION( "restart from tensor train complex" )
+    {
+        function f2=[&](double x) { return pow(x+0.1,5)+pow(x-0.5,4); };
+        auto exact = pow(1.1,6)/6-pow(0.1,6)/6 + pow(0.5,5)/5+pow(0.5,5)/5;
+
+        auto f=[&](vector<double> y) { return cmpx(f2(y[0]),f2(y[1])); };
+
+        auto ci=QTensorCI<cmpx>(f, grid::Quantics {0.0, 1.0, 40, 2, true});
+        ci.iterate(5);
+        ci.get_qtt().save("my_qtt.dat");
+
+        auto qtt=QTensorTrain<cmpx>::load("my_qtt.dat");
+        auto ci_2=QTensorCI<cmpx>(f, qtt.grid, qtt.tt);
+        auto res = ci_2.get_qtt().integral();
+        REQUIRE(std::abs(res - cmpx(exact,exact))<1e-9);
+    }
+
     SECTION( "copy pivots quantics" )
     {
         function f2=[&](double x) { return pow(x+0.1,5)+pow(x-0.5,4); };