title: Large matrix operations: Multiplication in Scala/Apache Spark
body: <p>I need to multiply two large matrices, <code>X</code> and <code>Y</code>.  Typically <code>X</code> has ~500K rows and ~18K columns and <code>Y</code> has ~18K rows and ~18K columns. The matrix <code>X</code> is expected to be sparse and the matrix <code>Y</code> is expected to be sparse/dense. What is the ideal way of performing this multiplication in Scala/Apache Spark?</p>