Java Jblas DoubleMatrix vector addition

Question

I feel really stupid asking this, but I can't find a method for adding a row/vector to an index or a specific set of indices.

My current workaround is to getRows(int[]) then addiRowVector(DoubleMatrix) then put(Range rs, Range cs, DoubleMatrix x) : (get rows, add your vector, then put them back)

This seems like a backwards and costly implementation, is there any alternative? Is there something simple I'm missing?

Thanks in advance!

Answer 1

For one row you can do it as in this piece of code using row number for example

void oneRow() {
    DoubleMatrix matrix = new DoubleMatrix(new double[][] {
            {11,12,13},
            {21,22,23},
            {31,32,33}});
    DoubleMatrix otherRow = new DoubleMatrix(new double[][] {{-11, -12, -13}});

    int rowNumber = 0;
    DoubleMatrix row = matrix.getRow(rowNumber);
    row.addiRowVector(otherRow);
    matrix.putRow(rowNumber, row);

    System.out.println(matrix);
}

as result you'll see

[0,000000, 0,000000, 0,000000; 21,000000, 22,000000, 23,000000; 31,000000, 32,000000, 33,000000]

for several rows you can use loop using row numbers array for example

void multipleRows() {
    DoubleMatrix matrix = new DoubleMatrix(new double[][] {
            {11,12,13},
            {21,22,23},
            {31,32,33}});

    int[] rowNumbers = {0, 2};
    DoubleMatrix otherRows = new DoubleMatrix(new double[][] {
            {-11, -12, -13},
            {-21, -22, -23}});
    int otherRowsNumber = 0;

    for (int r : rowNumbers) {
        DoubleMatrix row = matrix.getRow(r);
        row.addiRowVector(otherRows.getRow(otherRowsNumber++));
        matrix.putRow(r, row);
    }
    System.out.println(matrix);
}

and here for result you see

[0,000000, 0,000000, 0,000000; 21,000000, 22,000000, 23,000000; 10,000000, 10,000000, 10,000000]