--- /dev/null
+package jalview.math;
+
+import jalview.ext.android.SparseDoubleArray;
+
+/**
+ * A variant of Matrix intended for use for sparse (mostly zero) matrices. This
+ * class uses a SparseDoubleArray to hold each row of the matrix. The sparse
+ * array only stores non-zero values. This gives a smaller memory footprint, and
+ * fewer matrix calculation operations, for mostly zero matrices.
+ *
+ * @author gmcarstairs
+ */
+public class SparseMatrix extends Matrix
+{
+ /*
+ * we choose columns for the sparse arrays as this allows
+ * optimisation of the preMultiply() method used in PCA.run()
+ */
+ SparseDoubleArray[] sparseColumns;
+
+ /**
+ * Constructor given data in [row][column] order
+ *
+ * @param v
+ */
+ public SparseMatrix(double[][] v)
+ {
+ rows = v.length;
+ if (rows > 0) {
+ cols = v[0].length;
+ }
+ sparseColumns = new SparseDoubleArray[cols];
+
+ /*
+ * transpose v[row][col] into [col][row] order
+ */
+ for (int col = 0; col < cols; col++)
+ {
+ SparseDoubleArray sparseColumn = new SparseDoubleArray();
+ sparseColumns[col] = sparseColumn;
+ for (int row = 0; row < rows; row++)
+ {
+ double value = v[row][col];
+ if (value != 0d)
+ {
+ sparseColumn.put(row, value);
+ }
+ }
+ }
+ }
+
+ /**
+ * Answers the value at row i, column j
+ */
+ @Override
+ public double getValue(int i, int j)
+ {
+ return sparseColumns[j].get(i);
+ }
+
+ /**
+ * Sets the value at row i, column j to val
+ */
+ @Override
+ public void setValue(int i, int j, double val)
+ {
+ if (val == 0d)
+ {
+ sparseColumns[j].delete(i);
+ }
+ else
+ {
+ sparseColumns[j].put(i, val);
+ }
+ }
+
+ @Override
+ public double[] getColumn(int i)
+ {
+ double[] col = new double[height()];
+
+ SparseDoubleArray vals = sparseColumns[i];
+ for (int nonZero = 0; nonZero < vals.size(); nonZero++)
+ {
+ col[vals.keyAt(nonZero)] = vals.valueAt(nonZero);
+ }
+ return col;
+ }
+
+ @Override
+ public MatrixI copy()
+ {
+ double[][] vals = new double[height()][width()];
+ for (int i = 0; i < height(); i++)
+ {
+ vals[i] = getRow(i);
+ }
+ return new SparseMatrix(vals);
+ }
+
+ @Override
+ public MatrixI transpose()
+ {
+ double[][] out = new double[cols][rows];
+
+ /*
+ * for each column...
+ */
+ for (int i = 0; i < cols; i++)
+ {
+ /*
+ * put non-zero values into the corresponding row
+ * of the transposed matrix
+ */
+ SparseDoubleArray vals = sparseColumns[i];
+ for (int nonZero = 0; nonZero < vals.size(); nonZero++)
+ {
+ out[i][vals.keyAt(nonZero)] = vals.valueAt(nonZero);
+ }
+ }
+
+ return new SparseMatrix(out);
+ }
+
+ /**
+ * Answers a new matrix which is the product in.this. If the product contains
+ * less than 20% non-zero values, it is returned as a SparseMatrix, else as a
+ * Matrix.
+ * <p>
+ * This method is optimised for the sparse arrays which store column values
+ * for a SparseMatrix. Note that postMultiply is not so optimised. That would
+ * require redundantly also storing sparse arrays for the rows, which has not
+ * been done. Currently only preMultiply is used in Jalview.
+ */
+ @Override
+ public MatrixI preMultiply(MatrixI in)
+ {
+ if (in.width() != rows)
+ {
+ throw new IllegalArgumentException("Can't pre-multiply " + this.rows
+ + " rows by " + in.width() + " columns");
+ }
+ double[][] tmp = new double[in.height()][this.cols];
+
+ long count = 0L;
+ for (int i = 0; i < in.height(); i++)
+ {
+ for (int j = 0; j < this.cols; j++)
+ {
+ /*
+ * result[i][j] is the vector product of
+ * in.row[i] and this.column[j]
+ * we only need to use non-zero values from the column
+ */
+ SparseDoubleArray vals = sparseColumns[j];
+ boolean added = false;
+ for (int nonZero = 0; nonZero < vals.size(); nonZero++)
+ {
+ int myRow = vals.keyAt(nonZero);
+ double myValue = vals.valueAt(nonZero);
+ tmp[i][j] += (in.getValue(i, myRow) * myValue);
+ added = true;
+ }
+ if (added && tmp[i][j] != 0d)
+ {
+ count++; // non-zero entry in product
+ }
+ }
+ }
+
+ /*
+ * heuristic rule - if product is more than 80% zero
+ * then construct a SparseMatrix, else a Matrix
+ */
+ if (count * 5 < in.height() * cols)
+ {
+ return new SparseMatrix(tmp);
+ }
+ else
+ {
+ return new Matrix(tmp);
+ }
+ }
+
+ @Override
+ protected double divideValue(int i, int j, double divisor)
+ {
+ if (divisor == 0d)
+ {
+ return getValue(i, j);
+ }
+ double v = sparseColumns[j].divide(i, divisor);
+ return v;
+ }
+
+ @Override
+ protected double addValue(int i, int j, double addend)
+ {
+ double v = sparseColumns[j].add(i, addend);
+ return v;
+ }
+
+ /**
+ * Returns the fraction of the whole matrix size that is actually modelled in
+ * sparse arrays (normally, the non-zero values)
+ *
+ * @return
+ */
+ public float getFillRatio()
+ {
+ long count = 0L;
+ for (SparseDoubleArray col : sparseColumns)
+ {
+ count += col.size();
+ }
+ return count / (float) (height() * width());
+ }
+}
git://source.jalview.org / jalview.git / blobdiff