DoubleMatrices.java

package edu.berkeley.nlp.math;

public class DoubleMatrices {
/**
 * Returns the matrix transpose.  Assumes a non-empty rectangular matrix.
 */
	public static double[][] transpose(double[][] A) {
		double[][] B = new double[A[0].length][A.length];
		for (int i=0; i<B.length; i++) {
			for (int j=0; j<B[0].length; j++) {
				B[i][j] = A[j][i];
			}
		}
		return B;
	}
/**
 * Extracts column j and returns it as a single array.  Assumes a non-empty rectangular matrix.
 */
	public static double[] getColumnVector(double[][] A, int j) {
		double[] v = new double[A.length];
		for (int i=0; i<v.length; i++) {
			v[i] = A[i][j];
		}
		return v;
	}
	
	
/**
 * Returns the standard matrix product of two double matrices.
 */
	public static double[][] product(double[][] A, double[][] B) {
		if (A[0].length != B.length)
			throw new RuntimeException("cols in A (" + A.length +
					") differs from rows in B ( " + B.length + ")");
		double[][] C = new double[A.length][B[0].length];
		for (int i=0; i<A.length; i++) {
			for (int j=0; j<B[0].length; j++) {
				C[i][j] = DoubleArrays.innerProduct(A[i], DoubleMatrices.getColumnVector(B, j));
			}
		}
		return C;
	}

  public static double add(double[][] m) {
    double sum = 0.0;
    for (double[] row : m) {
      sum += DoubleArrays.add(row);
    }
    return sum;
  }

/**
 * Returns the matrix product v * B (v is treated as a row vector)
 */
	public static double[] product(double[] v, double[][] B) {
		double[][] A = new double[1][];
		A[0] = v;
		return product(A, B)[0];
	}

/**
 * Returns the matrix product A * v (v is treated as a column vector)
 */
	public static double[] product(double[][] A, double[] v) {
		double[][] B = new double[1][];
		B[0] = v;
		return transpose(product(A, transpose(B)))[0];
	}

  public static void normalizeEachRow(double[][] M) {
    for (double[] row : M) {
      DoubleArrays.probabilisticNormalize(row);
    }
  }

  public static void scale(double[][] M, double scale) {
    for (double[] row : M) {
      DoubleArrays.scale(row,scale);
    }
  }

  public static double[][] constantMatrix(double c, int m, int n) {
    double[][] M = new double[m][n];
    for (int i = 0; i < m; i++) {
      for (int j = 0; j < n; j++) {
        M[i][j] = c;
      }
    }
    return M;
  }
}