Github user mengxr commented on a diff in the pull request: https://github.com/apache/spark/pull/2294#discussion_r17709077 --- Diff: mllib/src/main/scala/org/apache/spark/mllib/linalg/Matrices.scala --- @@ -36,9 +37,42 @@ trait Matrix extends Serializable { /** Converts to a breeze matrix. */ private[mllib] def toBreeze: BM[Double] + /** Gets the i-th element in the array backing the matrix. */ + private[mllib] def apply(i: Int): Double + /** Gets the (i, j)-th element. */ - private[mllib] def apply(i: Int, j: Int): Double = toBreeze(i, j) + private[mllib] def apply(i: Int, j: Int): Double + + /** Return the index for the (i, j)-th element in the backing array. */ + private[mllib] def index(i: Int, j: Int): Int + + /** Update element at (i, j) */ + private[mllib] def update(i: Int, j: Int, v: Double) + + /** Get a deep copy of the matrix. */ + def copy: Matrix + + /** Convenience method for `Matrix`-`DenseMatrix` multiplication. */ + def times(y: DenseMatrix): DenseMatrix = { + val C: DenseMatrix = Matrices.zeros(numRows, y.numCols).asInstanceOf[DenseMatrix] + BLAS.gemm(false, false, 1.0, this, y, 0.0, C) + C + } + + /** Convenience method for `Matrix`-`DenseVector` multiplication. */ + def times(y: DenseVector): DenseVector = BLAS.gemv(1.0, this, y) + + /** Convenience method for `Matrix`^T^-`DenseMatrix` multiplication. */ + def transposeTimes(y: DenseMatrix): DenseMatrix = { --- End diff -- another approach is to have a boolean flag in matrix indicating whether it is transposed or not. ~~~ A.trans().times(y) ~~~
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