`get_unique_indices` not suitable for getting ToT intermediate indices

[Krzmbrzl]

As used in

SeQuant/SeQuant/core/eval_expr.cpp

Line 382 in 11a26e2

auto idxs = get_unique_indices(Product(ts));

this function is not suitable as it won't update proto-indices in case one of the proto-indices in an expression gets contracted.

This is illustrated by the current code producing:

I{a_3<i_2,i_3>,a_4<i_2,i_3>;i_1,i_2}:N-N-N = 3 f{i_3;i_1}:N-C-S * t{a_3<i_2,i_3>,a_4<i_2,i_3>;i_2,i_3}:N-C-S

where the proto indices should now be a_3<i_2,i_1> and a_2<i_2,i_1>.

/CC @bimalgaudel

[bimalgaudel]

Where is this example from? Is it arbitrary for illustration purpose?

[Krzmbrzl]

It's from TA eval tests:

SeQuant/tests/unit/test_eval_ta.cpp

Lines 776 to 796 in c9607cf

	SECTION("T_times_ToT_to_ToT") {
	constexpr std::wstring_view expr_str =
	L"3"
	L" * "
	L"f{i3;i1}"
	L" * "
	L"t{a3<i2,i3>,a4<i2,i3>;i2,i3}";
	auto const node = eval_node(parse_expr(expr_str));
	std::string const target_layout{"i_1,i_2,i_3;a_3i_2i_3,a_4i_2i_3"};
	auto result = evaluate(node, target_layout, yield)->get<ArrayToT>();
	ArrayToT ref;
	{
	auto const& lhs = yield(L"f{i3;i1}")->get<ArrayT>();
	auto const& rhs =
	yield(L"t{a3<i2,i3>,a4<i2,i3>;i2,i3}")->get<ArrayToT>();
	ref = TA::einsum(lhs("i_3,i_1"), rhs("i_2,i_3;a_3i_2i_3,a_4i_2i_3"),
	target_layout);
	ref(target_layout) = 3 * ref(target_layout);
	}
	REQUIRE(approx_equal("i,j,k;a,b", result, ref));
	}

what I wrote above is the stringified version of node