Thread Subject: Problem with grid of Nichols plot

hi,

I want to plot an function with nichols
My function is >> F=tf([23.7],[0.0081 1 0])
Then >> nichols(F),ngrid

It works with no problem, but I want to modify the grid
I have the grid for 6dB, 3dB, 1dB
I just want to have a grid for 2.3dB.

How can I dot it ?

thanks

"Cedric Cedric" <cedric.mathieu@ires.in2p3.fr> wrote in message <gkhj16$cjn$1@fred.mathworks.com>...
>...
> I just want to have a grid for 2.3dB.

You can have a grid for 2.3dB by modifying "nicchart.m" as follows;

1.
% Gain points (in dB)
g1 = [6 3 2 1 .75 .5 .4 .3 .25 .2 .15 .1 .05 0 -.05 -.1 ...
      -.15 -.2 -.25 -.3 -.4 -.5 -.75 -1 -2 -3 -4 -5 -6 -9 ...
      -12 -16 -20:-10:max(-40,gmin) gmin(:,gmin<-40)];
------>

% Gain points (in dB)
g1 = [6 3 2.3 2 1 .75 .5 .4 .3 .25 .2 .15 .1 .05 0 -.05 -.1 ...
      -.15 -.2 -.25 -.3 -.4 -.5 -.75 -1 -2 -3 -4 -5 -6 -9 ...
      -12 -16 -20:-10:max(-40,gmin) gmin(:,gmin<-40)];
2.
% (2) Generate isogain lines for following gain values:
g2 = [6 3 1 .5 .25 0 -1 -3 -6 -12 -20 -40:-20:gmin];
------>
% (2) Generate isogain lines for following gain values:
g2 = [6 3 2.3 1 .5 .25 0 -1 -3 -6 -12 -20 -40:-20:gmin];

The M-file, "nicchart.m", can be found in "(MATLAB folder)\toolbox\control\ctrlguis."