black - Black's diagram (Nichols chart)
Black's diagram (Nichols'chart) for a linear system sl. sl can be a continuous-time or discrete-time SIMO system (see syslin). In case of multi-output the outputs are plotted with different symbols.
The frequencies are given by the bounds fmin,fmax (in Hz) or by a row-vector (or a matrix for multi-output) frq.
step is the ( logarithmic ) discretization step. (see calfrq for the choice of default value).
comments is a vector of character strings (captions).
db,phi are the matrices of modulus (in Db) and phases (in degrees). (One row for each response).
repf matrix of complex numbers. One row for each response.
To plot the grid of iso-gain and iso-phase of y/(1+y) use chart().
Default values for fmin and fmax are 1.d-3, 1.d+3 if sl is continuous-time or 1.d-3, 0.5 if sl is discrete-time.
s=poly(0,'s')
h=syslin('c',(s^2+2*0.9*10*s+100)/(s^2+2*0.3*10.1*s+102.01))
chart();
sstr='(s^2+2*0.9*10*s+100)/(s^2+2*0.3*10.1*s+102.01)';
black(h,0.01,100,sstr);
h1=h*syslin('c',(s^2+2*0.1*15.1*s+228.01)/(s^2+2*0.9*15*s+225))
xbasc()
black([h1;h],0.01,100,['h1';'h'])