A lot of effort has gone into brining this book into the present shape. The text is based on the lectures to our students during the past 20 years. The language of the book has been kept simple and self-explanatory. Those who deserve our appreciation are innumerable but we would like to thank the following who have in one way or the other contributed to this book:
To Dr Sandeep Sharma, Dr Sarika Sharma, and Dr Vikas Sharma for reading the manuscript.
To Sohan Lal Bansal who has done an excellent job of preparing all the diagrams in the book.
To Dr S K Kaushal for his kind support.
To Shri Rama Shankar Singh, Chairman, ITM Group of Institutions at Gwalior, for his continuous support and inspiration since 2003.
To our senior management, ...