automatically download nonzero datatype metadata

lib/matrix.py

@@ -0,0 +1,17 @@
+class Matrix:
+    def __init__(self, group, name, dtype, nrows, ncols, nnz):
+        self.group = group
+        self.name = name
+        self.dtype = dtype
+        self.nrows = int(nrows)
+        self.ncols = int(ncols)
+        self.nnz = int(nnz)
+
+    def to_tuple(self):
+        return (self.group, self.name, self.dtype, self.nrows, self.ncols, self.nnz)
+
+    def __repr__(self):
+        return repr(self.to_tuple())
+
+    def url(self):
+        return "/".join(("https://sparse.tamu.edu", "MM", self.group, self.name + ".tar.gz"))