matrix market reader post

content/post/20210730-mm/index.md

@@ -0,0 +1,105 @@
++++
+title = "Single-header C++ Matrix Market Reader"
+date = 2021-07-30T00:00:00
+lastmod = 2021-07-30T00:00:00
+draft = false
+
+# Authors. Comma separated list, e.g. `["Bob Smith", "David Jones"]`.
+authors = ["Carl Pearson"]
+
+tags = ["sparse"]
+
+summary = "GPLv3 single-header C++11 Matrix Market Reader"
+
+# Projects (optional).
+#   Associate this post with one or more of your projects.
+#   Simply enter your project's folder or file name without extension.
+#   E.g. `projects = ["deep-learning"]` references 
+#   `content/project/deep-learning/index.md`.
+#   Otherwise, set `projects = []`.
+projects = []
+
+# Featured image
+# To use, add an image named `featured.jpg/png` to your project's folder. 
+[image]
+  # Caption (optional)
+  caption = ""
+
+  # Focal point (optional)
+  # Options: Smart, Center, TopLeft, Top, TopRight, Left, Right, BottomLeft, Bottom, BottomRight
+  focal_point = "Center"
+
+  # Show image only in page previews?
+  preview_only = true
+
+
+categories = []
+
+# Set captions for image gallery.
+
+
++++
+
+I'm continually re-writing some C++ code to read [Matrix Market files](https://math.nist.gov/MatrixMarket/formats.html), a common format for distributing matrices.
+I finally got around to writing something that I should be able to reuse.
+
+The code is [available on github](github.com/cwpearson/matrix-market).
+
+An example follows:
+
+```c++
+#include "mm/mm.hpp"
+
+int main(int argc, char **argv)
+{
+    if (argc < 2)
+    {
+        std::cerr << "Usage: " << argv[0] << " <file.mtx>\n";
+        exit(EXIT_FAILURE);
+    }
+    const std::string path = argv[1];
+
+    {
+        std::cout << "with Ordinal=int, Scalar=float, Offset=size_t" << std::endl;
+        typedef int Ordinal;
+        typedef float Scalar;
+        typedef MtxReader<Ordinal, Scalar> reader_t;
+        typedef typename reader_t::coo_type coo_t;
+        typedef typename coo_t::entry_type entry_t;
+
+        // read matrix as coo
+        reader_t reader(path);
+        coo_t coo = reader.read_coo();
+
+        // non-zeros, rows, cols
+        std::cout << coo.nnz() << std::endl;                               // size_t
+        std::cout << coo.num_rows() << "," << coo.num_cols() << std::endl; // int
+
+        // first entry
+        entry_t e = coo.entries[0];
+        std::cout << e.i << "," << e.j << std::endl; // int, int
+        std::cout << e.e << std::endl;               // float
+    }
+
+    {
+        std::cout << "with Ordinal=int64_t, Scalar=std::complex<float>, Offset=int" << std::endl;
+        typedef MtxReader<int64_t, std::complex<float>, int> reader_t;
+        typedef typename reader_t::coo_type coo_t;
+        typedef typename coo_t::entry_type entry_t;
+
+        // read matrix as coo
+        reader_t reader(path);
+        coo_t coo = reader.read_coo();
+
+        // non-zeros, rows, cols
+        std::cout << coo.nnz() << std::endl;                               // int
+        std::cout << coo.num_rows() << "," << coo.num_cols() << std::endl; // complex<double>
+
+        // first entry
+        entry_t e = coo.entries[0];
+        std::cout << e.i << "," << e.j << std::endl; // int64_t
+        std::cout << e.e << std::endl;               // complex<double>
+    }
+    return 0;
+}
+```