Function sigrid: Plotting the sigma Requirement on a Root Locus
Below is the function sigrid.m. This function will plot the sigma requirement on the same graph as another plot, such as a root locus plot generated with the rlocus command. To employ sigrid.m in MATLAB, use the syntax sigrid(sigma). Copy the following text into a file sigrid.m, and put it in the same directory as the MATLAB software, or in a directory which is contained in MATLAB's search path.
function[ ] = sigrid(sig) %SIGRID Generate s-plane grid lines for a root locus or pole-zero map. % % SIGRID generates a grid over an existing continuous s-plane root % locus or pole-zero map. Lines of constant sigma are drawn in. % To be used with SGRID if sigma, zeta, and Wn requirements are required % simultaneously. Can also be used by itself. % % See also: RLOCUS, ZGRID, SGRID, and PZMAP. error(nargchk(1,1,nargin)); hold on %Plot sigma line limits = axis; mx=limits(1,4); mn=limits(1,3); stz=abs(mx)+abs(mn); st=stz/50; im=mn:st:mx; lim=length(im); for i=1:lim re(i)=-sig; end re(:); plot(re,im,'.') hold off return