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Add AutoMPO concat function for local operators #229

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Add AutoMPO concat function for local operators #229

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46 changes: 44 additions & 2 deletions itensor/mps/autompo.h
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Original file line number Diff line number Diff line change
Expand Up @@ -190,10 +190,11 @@ class AutoMPO

public:

AutoMPO() { }
AutoMPO(): concatAccumulator(nullptr)
{ }

AutoMPO(SiteSet const& sites)
: sites_(sites)
: sites_(sites), concatAccumulator(nullptr)
{ }

SiteSet const&
Expand All @@ -213,11 +214,52 @@ class AutoMPO
Accumulator
operator+=(T x) { return Accumulator(this,x); }

template <typename T>
AutoMPO&
concat(T x)
{
if (concatAccumulator==nullptr)
{
concatAccumulator = new Accumulator(this,x);
}
else { (*concatAccumulator),x; }

return *this;
}

template <typename T, typename... VarArgs>
AutoMPO&
concat(T first, VarArgs... vargs)
{
if (concatAccumulator==nullptr)
{
concatAccumulator = new Accumulator(this,first);
return concat(vargs...);
}
else
{
(*concatAccumulator),first;
return concat(vargs...);
}
}

//this calls add with the completed accumulator
void combine()
{
delete concatAccumulator;
concatAccumulator=nullptr;
}

void
add(HTerm const& t);

void
reset() { terms_.clear(); }

private:

//temporary accumulator for concat
Accumulator* concatAccumulator;
};

std::ostream&
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72 changes: 72 additions & 0 deletions unittest/autompo_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -328,6 +328,78 @@ SECTION("Single Site Ops")
// }
}

SECTION("Concat")
{
int L = 10;
auto sites = Hubbard(L);

SECTION("Diagonal op")
{
auto ampo = AutoMPO(sites);
auto n = 4;
//ampo += "Nup",n;
ampo.concat("Nup",n).combine();
auto Op = IQMPO(ampo);
for(auto i : range1(L))
{
auto state = InitState(sites,"Emp");
state.set(i,"Up");
auto psi = IQMPS(state);
auto x = overlap(psi,Op,psi);
if(i == n) CHECK_CLOSE(x,1.);
else CHECK_CLOSE(x,0.);
}
}
SECTION("Concat MPO For Loop")
{
auto ampo = AutoMPO(sites);
ampo += 0.5,"Nup",1,"Nup",2,"Nup",3,"Nup",4;
auto correct = MPO(ampo);
auto norm = overlap(correct,correct);

auto ampoC = AutoMPO(sites);
ampoC.concat(0.5);
for(auto i : range1(4))
{
ampoC.concat("Nup",i);
}
ampoC.combine();
auto C = MPO(ampoC);
CHECK_CLOSE(overlap(correct,C),norm);

auto state = InitState(sites,"Up");
auto psi = MPS(state);

CHECK_CLOSE(overlap(psi,C,psi),overlap(psi,correct,psi));
}

SECTION("Concat IQMPO chained")
{
auto ampo = AutoMPO(sites);
ampo += 1.0,"Nup",1,"Sz",2,"Nup",3,"Sz",4;
ampo += 1.0,"Sz",1,"Nup",2,"Sz",3,"Nup",4;
auto correct = IQMPO(ampo);
auto norm = overlap(correct,correct);

auto ampoC = AutoMPO(sites);
ampoC.concat(1.0,"Nup",1)
.concat("Sz",2,"Nup",3)
.concat("Sz",4)
.combine();
ampoC.concat(1.0,"Sz",1)
.concat("Nup",2,"Sz",3)
.concat("Nup",4)
.combine();
auto C = IQMPO(ampoC);
CHECK_CLOSE(overlap(correct,C),norm);

auto state = InitState(sites,"Up");
auto psi = IQMPS(state);

CHECK_CLOSE(overlap(psi,C,psi),overlap(psi,correct,psi));
}
}

SECTION("toExpH ITensor")
{
int N = 10;
Expand Down