From 7e029d1d6ec0eba495a31c72a328ee8160338e44 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Mon, 29 Aug 2016 12:06:37 +0200
Subject: bug #1271: add SparseMatrix::coeffs() methods returning a 1D view of
 the non zero coefficients.

---
 Eigen/src/SparseCore/SparseCompressedBase.h | 19 +++++++++++++++++++
 doc/snippets/SparseMatrix_coeffs.cpp        |  9 +++++++++
 test/sparse_basic.cpp                       | 10 ++++++++++
 3 files changed, 38 insertions(+)
 create mode 100644 doc/snippets/SparseMatrix_coeffs.cpp

diff --git a/Eigen/src/SparseCore/SparseCompressedBase.h b/Eigen/src/SparseCore/SparseCompressedBase.h
index 15854a73b..55ad91f46 100644
--- a/Eigen/src/SparseCore/SparseCompressedBase.h
+++ b/Eigen/src/SparseCore/SparseCompressedBase.h
@@ -106,6 +106,25 @@ class SparseCompressedBase
     /** \returns whether \c *this is in compressed form. */
     inline bool isCompressed() const { return innerNonZeroPtr()==0; }
 
+    /** \returns a read-only view of the stored coefficients as a 1D array expression.
+      *
+      * \warning this method is for \b compressed \b storage \b only, and it will trigger an assertion otherwise.
+      *
+      * \sa valuePtr(), isCompressed() */
+    const Map<const Array<Scalar,Dynamic,1> > coeffs() const { eigen_assert(isCompressed()); return Array<Scalar,Dynamic,1>::Map(valuePtr(),nonZeros()); }
+
+    /** \returns a read-write view of the stored coefficients as a 1D array expression
+      *
+      * \warning this method is for \b compressed \b storage \b only, and it will trigger an assertion otherwise.
+      *
+      * Here is an example:
+      * \include SparseMatrix_coeffs.cpp
+      * and the output is:
+      * \include SparseMatrix_coeffs.out
+      *
+      * \sa valuePtr(), isCompressed() */
+    Map<Array<Scalar,Dynamic,1> > coeffs() { eigen_assert(isCompressed()); return Array<Scalar,Dynamic,1>::Map(valuePtr(),nonZeros()); }
+
   protected:
     /** Default constructor. Do nothing. */
     SparseCompressedBase() {}
diff --git a/doc/snippets/SparseMatrix_coeffs.cpp b/doc/snippets/SparseMatrix_coeffs.cpp
new file mode 100644
index 000000000..f71a69b07
--- /dev/null
+++ b/doc/snippets/SparseMatrix_coeffs.cpp
@@ -0,0 +1,9 @@
+SparseMatrix<double> A(3,3);
+A.insert(1,2) = 0;
+A.insert(0,1) = 1;
+A.insert(2,0) = 2;
+A.makeCompressed();
+cout << "The matrix A is:" << endl << MatrixXd(A) << endl;
+cout << "it has " << A.nonZeros() << " stored non zero coefficients that are: " << A.coeffs().transpose() << endl;
+A.coeffs() += 10;
+cout << "After adding 10 to every stored non zero coefficient, the matrix A is:" << endl << MatrixXd(A) << endl;
diff --git a/test/sparse_basic.cpp b/test/sparse_basic.cpp
index 10309b3a9..7b5f3eb38 100644
--- a/test/sparse_basic.cpp
+++ b/test/sparse_basic.cpp
@@ -207,6 +207,16 @@ template<typename SparseMatrixType> void sparse_basic(const SparseMatrixType& re
     VERIFY_IS_APPROX((m1 = m1.transpose()), (refM1 = refM1.transpose().eval()));
     VERIFY_IS_APPROX((m1 = -m1.transpose()), (refM1 = -refM1.transpose().eval()));
     VERIFY_IS_APPROX((m1 += -m1), (refM1 += -refM1));
+
+    if(m1.isCompressed())
+    {
+      VERIFY_IS_APPROX(m1.coeffs().sum(), m1.sum());
+      m1.coeffs() += s1;
+      for(Index j = 0; j<m1.outerSize(); ++j)
+        for(typename SparseMatrixType::InnerIterator it(m1,j); it; ++it)
+          refM1(it.row(), it.col()) += s1;
+      VERIFY_IS_APPROX(m1, refM1);
+    }
   }
 
   // test transpose
-- 
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