public override string ToString()
{
StringBuilder sb = new StringBuilder();
sb.AppendFormat( " | {0} {1} {2} {3} |\n", this.m00, this.m01, this.m02, this.m03 );
sb.AppendFormat( " | {0} {1} {2} {3} |\n", this.m10, this.m11, this.m12, this.m13 );
sb.AppendFormat( " | {0} {1} {2} {3} |\n", this.m20, this.m21, this.m22, this.m23 );
sb.AppendFormat( " | {0} {1} {2} {3} |\n", this.m30, this.m31, this.m32, this.m33 );
return sb.ToString();
}