C# code

The code is supposed to multiply a matrix by a scalar value and then print it out to the Matrix to the Console....
I know that a double Array is used and then each of the values of a is multiplied by b....
What does the code do after the a*= b;  line? 
Is StringWriter some type of a function and strOut is the name of it?      (Also, there is some type of error in the code, can you identify it?). Thanks in advance. 
static void Main()
{

   double[,] a;
   a = new double[,] { { 1, 2, 5 }, { 7, -3, 8 } };
   double b = 2.3;

a *= b;

   StringWriter strOut = new StringWriter();
   strOut.Write("Matrix is:");

   for (int i = 0; i < a.GetLength(0); i++)
   {

      strOut.WriteLine();
      for (int j = 0; j < a.GetLength(1); j++)
      {

          strOut.Write("{0,9:f3}", a[i, j]);
      }

}

   Console.WriteLine(strOut.ToString());
}