code: function (b) {
              b = b.val;
              var a = this.val,
                  a0 = a[0],
                  a1 = a[1],
                  a3 = a[3],
                  a4 = a[4],
                  b0 = b[0],
                  b1 = b[1],
                  b3 = b[3],
                  b4 = b[4],
                  b6 = b[6],
                  b7 = b[7];
  
              a[0] = a0 * b0 + a3 * b1;
              a[1] = a1 * b0 + a4 * b1;
              a[3] = a0 * b3 + a3 * b4;
              a[4] = a1 * b3 + a4 * b4;
              a[6] += a0 * b6 + a3 * b7;
              a[7] += a1 * b6 + a4 * b7;
  
              return this;
          }
docs: multiply both matrix
  @name multiply
  @memberOf me.Matrix2d
  @function
  @param {me.Matrix2d} b Other matrix
  @return {me.Matrix2d} Reference to this object for method chaining