Custom contraction

include/tensorwrapper/detail_/dsl_base.hpp

@@ -61,6 +61,9 @@ class DSLBase {
     /// Type of parsed labels
     using label_type = typename labeled_type::label_type;
 
+    /// Type of a mutable reference to a labeled_type object
+    using labeled_reference = labeled_type&;
+
     /// Type of a read-only reference to a labeled_type object
     using const_labeled_reference = const labeled_const_type&;
 

include/tensorwrapper/dsl/dummy_indices.hpp

@@ -15,6 +15,7 @@
  */
 
 #pragma once
+#include <ostream>
 #include <set>
 #include <string>
 #include <utilities/containers/indexable_container_base.hpp>
@@ -110,6 +111,15 @@ class DummyIndices
       DummyIndices(
         utilities::strings::split_string(remove_spaces_(dummy_indices), ",")) {}
 
+    /// Main ctor for setting the value, throws if any index is empty
+    explicit DummyIndices(split_string_type split_dummy_indices) :
+      m_dummy_indices_(std::move(split_dummy_indices)) {
+        for(const auto& x : m_dummy_indices_)
+            if(x.empty())
+                throw std::runtime_error(
+                  "Dummy index is not allowed to be empty");
+    }
+
     /** @brief Determines the number of unique indices in *this.
      *
      *  A dummy index can be repeated if it is going to be summed over. This
@@ -212,12 +222,27 @@ class DummyIndices
      *
      *  Each DummyIndices object is viewed as an ordered set of objects. If
      *  two DummyIndices objects contain the same objects, but in a different
-     *  order, we can convert either object into the other by permuting it.
-     *  This method computes the permutation needed to change *this into
-     *  @p other. More specifically the result of this method is a vector
-     *  of length `size()` such that the `i`-th element is the offset of
-     *  `(*this)[i]` in @p other, i.e., if `x` is the return then
-     *  `other[x[i]] ==  (*this)[i]`.
+     *  order, we can convert either object into the other by permuting it. This
+     *  method determines the permutation necessary to convert *this into other;
+     *  the reverse permutation, i.e., converting other to *this is obtained
+     *  by `other.permutation(*this)`.
+     *
+     *  For concreteness assume we have a set A=(i, j, k) and we want to
+     *  permute it into the set B=(j,k,i), then there are two subtly different
+     *  ways of writing the necessary permutation:
+     *  1. Write the target set in terms of the current offsets, e.g., A goes
+     *     to B is written as P1=(1, 2, 0)
+     *  2. Write the current set in terms of the target offsets, e.g., A goes
+     *     to B is written as P2=(2, 0, 1)
+     *
+     *  Option one maps offsets in B to offsets in A, e.g., A[P1[0]] == B[0],
+     *  whereas option two maps offsets in A to offsets in B, e.g.,
+     *  A[0] == B[P2[0]]. This method follows definition two.
+     *
+     *  @note The definitions are inverses of each other. So if you don't like
+     *  our definition, and want the other one, flip *this and @p other, e.g.,
+     *  Permuting B to A using definition 1 yields P1'=(2, 0, 1)=P2  and
+     *  permuting B to A using definition 1 yields P2'=(1, 2, 0)=P1.
      *
      *  @param[in] other The order we want to permute *this to.
      *
@@ -437,15 +462,6 @@ class DummyIndices
     }
 
 protected:
-    /// Main ctor for setting the value, throws if any index is empty
-    explicit DummyIndices(split_string_type split_dummy_indices) :
-      m_dummy_indices_(std::move(split_dummy_indices)) {
-        for(const auto& x : m_dummy_indices_)
-            if(x.empty())
-                throw std::runtime_error(
-                  "Dummy index is not allowed to be empty");
-    }
-
     /// Lets the base class get at these implementations
     friend base_type;
 
@@ -471,6 +487,17 @@ class DummyIndices
     split_string_type m_dummy_indices_;
 };
 
+template<typename StringType>
+std::ostream& operator<<(std::ostream& os, const DummyIndices<StringType>& i) {
+    if(i.size() == 0) return os;
+    os << i.at(0);
+    for(std::size_t j = 1; j < i.size(); ++j) {
+        os << ",";
+        os << i.at(j);
+    }
+    return os;
+}
+
 template<typename StringType>
 bool DummyIndices<StringType>::is_hadamard_product(
   const DummyIndices& lhs, const DummyIndices& rhs) const noexcept {

src/tensorwrapper/buffer/contraction_planner.hpp

@@ -0,0 +1,130 @@
+/*
+ * Copyright 2025 NWChemEx-Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+#include <tensorwrapper/dsl/dummy_indices.hpp>
+
+namespace tensorwrapper::buffer {
+
+/** @brief Class for working out details pertaining to a tensor contraction.
+ *
+ *  N.B. Contraction covers direct product (which is a special case of
+ *  contraction with 0 dummy indices).
+ */
+class ContractionPlanner {
+public:
+    /// String type users use to label modes
+    using string_type = std::string;
+
+    /// Type of the parsed labels
+    using label_type = dsl::DummyIndices<string_type>;
+
+    ContractionPlanner(string_type result, string_type lhs, string_type rhs) :
+      ContractionPlanner(label_type(result), label_type(lhs), label_type(rhs)) {
+    }
+
+    ContractionPlanner(label_type result, label_type lhs, label_type rhs) :
+      m_result_(std::move(result)),
+      m_lhs_(std::move(lhs)),
+      m_rhs_(std::move(rhs)) {
+        assert_no_repeated_indices_();
+        assert_dummy_indices_are_similar_();
+        assert_no_shared_free_();
+    }
+
+    /// Labels in LHS that are NOT summed over
+    label_type lhs_free() const { return m_lhs_.intersection(m_result_); }
+
+    /// Labels in RHS that are NOT summed over
+    label_type rhs_free() const { return m_rhs_.intersection(m_result_); }
+
+    /// Labels in LHS that ARE summed over
+    label_type lhs_dummy() const { return m_lhs_.difference(m_result_); }
+
+    /// Labels in RHS that ARE summed over
+    label_type rhs_dummy() const { return m_rhs_.difference(m_result_); }
+
+    /** @brief LHS permuted so free indices are followed by dummy indices. */
+    label_type lhs_permutation() const {
+        using split_string_type = typename label_type::split_string_type;
+        split_string_type rv;
+        auto lfree  = lhs_free();
+        auto ldummy = lhs_dummy();
+        for(const auto& freei : m_result_) {
+            if(!lfree.count(freei)) continue;
+            rv.push_back(freei);
+        }
+        for(const auto& dummyi : ldummy) rv.push_back(dummyi);
+        return label_type(std::move(rv));
+    }
+
+    /** @brief RHS permuted so dummy indices are followed by free indices. */
+    label_type rhs_permutation() const {
+        typename label_type::split_string_type rv;
+        auto rfree  = rhs_free();
+        auto rdummy = lhs_dummy(); // Use LHS dummy to get the same order!
+        for(const auto& dummyi : rdummy)
+            rv.push_back(dummyi); // Know it only appears 1x
+        for(const auto& freei : m_result_) {
+            if(!rfree.count(freei)) continue;
+            rv.push_back(freei); // Know it only appears 1x
+        }
+        return label_type(std::move(rv));
+    }
+
+    /** @brief Flattened result labels.
+     *
+     *  After applying lhs_permutation to LHS to get A, and rhs_permutation to
+     *  RHS to get B, A and B can be multiplied together with a gemm. The
+     *  resulting matrix has indices given by concatenating the free indices of
+     *  A with the free indices of B. This method returns those indices.
+     *
+     */
+    label_type result_matrix_labels() const {
+        const auto lhs = lhs_permutation();
+        const auto rhs = rhs_permutation();
+        return lhs.concatenation(rhs).difference(lhs_dummy());
+    }
+
+private:
+    /// Ensures no tensor contains a repeated label
+    void assert_no_repeated_indices_() const {
+        const bool result_good = !m_result_.has_repeated_indices();
+        const bool lhs_good    = !m_lhs_.has_repeated_indices();
+        const bool rhs_good    = !m_rhs_.has_repeated_indices();
+
+        if(result_good && lhs_good && rhs_good) return;
+        throw std::runtime_error("One or more terms contain repeated labels");
+    }
+
+    /// Ensures the dummy indices are permutations of each other
+    void assert_dummy_indices_are_similar_() const {
+        if(lhs_dummy().is_permutation(rhs_dummy())) return;
+        throw std::runtime_error("Dummy indices must appear in all terms");
+    }
+
+    /// Asserts LHS and RHS do not share free indices, which is Hadamard-product
+    void assert_no_shared_free_() const {
+        if(!lhs_free().intersection(rhs_free()).size()) return;
+        throw std::runtime_error("Contraction must sum repeated indices");
+    }
+
+    label_type m_result_;
+    label_type m_lhs_;
+    label_type m_rhs_;
+};
+
+} // namespace tensorwrapper::buffer

src/tensorwrapper/buffer/eigen.cpp

@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 #include "eigen_contraction.hpp"
 #include <sstream>
 #include <tensorwrapper/allocator/eigen.hpp>
@@ -139,7 +140,8 @@ typename EIGEN::dsl_reference EIGEN::permute_assignment_(
     const auto& rlabels = rhs.labels();
 
     if(this_labels != rlabels) { // We need to permute rhs before assignment
-        auto r_to_l = rhs.labels().permutation(this_labels);
+        // Eigen adopts the opposite definition of permutation from us.
+        auto r_to_l = this_labels.permutation(rlabels);
         // Eigen wants int objects
         std::vector<int> r_to_l2(r_to_l.begin(), r_to_l.end());
         m_tensor_ = rhs_downcasted.value().shuffle(r_to_l2);
@@ -226,28 +228,7 @@ typename EIGEN::dsl_reference EIGEN::hadamard_(label_type this_labels,
 TPARAMS typename EIGEN::dsl_reference EIGEN::contraction_(
   label_type this_labels, const_labeled_reference lhs,
   const_labeled_reference rhs) {
-    const auto& llabels = lhs.labels();
-    const auto& lobject = lhs.object();
-    const auto& rlabels = rhs.labels();
-    const auto& robject = rhs.object();
-
-    // N.b. is a pure contraction, so common indices are summed over
-    auto common = llabels.intersection(rlabels);
-
-    // -- This block converts string indices to mode offsets
-    using rank_type = unsigned short;
-    using pair_type = std::pair<rank_type, rank_type>;
-    std::vector<pair_type> modes;
-    auto rank = common.size();
-    for(decltype(rank) i = 0; i < rank; ++i) {
-        const auto& index_i = common.at(i);
-        // N.b., pure contraction so there's no repeats within a tensor's label
-        auto lindex = llabels.find(index_i)[0];
-        auto rindex = rlabels.find(index_i)[0];
-        modes.push_back(pair_type(lindex, rindex));
-    }
-
-    return eigen_contraction<FloatType>(*this, lobject, robject, modes);
+    return eigen_contraction(*this, this_labels, lhs, rhs);
 }
 
 #undef EIGEN