ph-math/src/main/java/com/helger/numbercruncher/matrix/Matrix.java
public Matrix multiply (final Matrix m) throws MatrixException
  {
    // Validate m's dimensions.
    if (m_nCols != m.m_nRows)
    {
      throw new MatrixException (MatrixException.INVALID_DIMENSIONS);
    }

    final float pv[][] = new float [m_nRows] [m.m_nCols]; // product values

    // Compute values of the product.
    for (int r = 0; r < m_nRows; ++r)
    {
      for (int c = 0; c < m.m_nCols; ++c)
      {
        float dot = 0;
        for (int k = 0; k < m_nCols; ++k)
        {
          dot += m_aValues[r][k] * m.m_aValues[k][c];
        }
        pv[r][c] = dot;
      }
    }

    return new Matrix (pv);
  }
public Matrix multiply (final Matrix m) throws MatrixException
  {
    // Validate m's dimensions.
    if (m_nCols != m.m_nRows)
    {
      throw new MatrixException (MatrixException.INVALID_DIMENSIONS);
    }

    final float pv[][] = new float [m_nRows] [m.m_nCols]; // product values

    // Compute values of the product.
    for (int r = 0; r < m_nRows; ++r)
    {
      for (int c = 0; c < m.m_nCols; ++c)
      {
        float dot = 0;
        for (int k = 0; k < m_nCols; ++k)
        {
          dot += m_aValues[r][k] * m.m_aValues[k][c];
        }
        pv[r][c] = dot;
      }
    }

    return new Matrix (pv);
  }
Multiply this matrix by another matrix.

@param m
the matrix multiplier
@return the product matrix
@throws MatrixException
for invalid size