http://www.cds.caltech.edu/~murray/courses/cds101/fa03/caltech/am03_ch7-7nov03.pdf

http://www.sutech.ac.ir/Portal/channels/FcKUploadedFiles/fa/1025/Documents/Modern%20Control%20Engineering%20Problems%20Ch%208.pdf

http://www.cds.caltech.edu/~murray/books/AM08/pdf/am08-analysis_19Jul11.pdf

https://doc-0c-8g-docsviewer.googleusercontent.com/viewer/securedownload/dsn1aovipa7l846lsfcf94nedj8q2p4u/pmdbihedvpi0ji01edniv3g6b37gf1mv/1357380000000/dXJs/AGZ5hq8BgbJY1gwaOYx83cPOdNw6/aHR0cDovL3d3dy5lY2UucnV0Z2Vycy5lZHUvfmdhamljL3BzZmlsZXMvbnlxdWlzdC5wZGY=?docid=f750db088d5f63ffb412c0f6b79f09da&chan=EwAAAHqElQfRPdMwE/xHe/4ACNlKndh3P9XopPP8uoRAL7WL&sec=AHSqidY3ZuAUPB5AmS1ea4aI_SU_IEKx1UJo5EtOhBwDoxnLgmrxeN4SiWeusNy6PP8-r0KMNQ2N&a=gp&filename=nyquist.pdf&nonce=hfbmle3qf3kla&user=AGZ5hq8BgbJY1gwaOYx83cPOdNw6&hash=n4mqlr66q4nai33muic0ff4jha5kafen

http://www.wosco.org/books/StabilityTheory.pdf

http://books.google.com/books/about/Feedback_Control_Systems.html?id=WztCGcPo0xIC