Re: Forming Cell of systems

[Thomas D. Dean]

On 06/13/15 12:42, Thomas D. Dean wrote:
> I am having problems forming a cell array of transfer functions.  I
> believe the problem is in my lack of understanding cellfun.
>
> In matlab, I would
>
> A0 = 10;
> b = 1 / A0;    % approximation for ab>>1
> R1 = 10000;
> R2 = R1 * (1/b - 1)
> K = R1/(R1+R2);
> C = [1:.2:3]*1e-12;
> for n = 1:length(C)
>      b_array(:,:,n) = tf([K*R2*C(n) K],[K*R2*C(n) 1]);
> end
>
> I want to create a cell array, so I tried
>
> b_array=cellfun(@tf,{[K*R2*C K]},{[K*R2*C 1]})
>
> This creates an array with one entry, when I wanted an array of 11
> transfer functions.

I finished a preamp using ngspice and thought I could duplicate the 
numbers with the control package.  I sort-of can do it, but, I can not 
seem to get some of the package functions either create cell arrays of 
the correct shape or accept cell arrays as arguments.

I tried some other options with no success other than looping. 
According to the way I read help cellfun, I should be able to create a 
cell array of transfer functions with one line of code.  But, I can not.

The plot I want to produce is:
###################################################
a0 = 1e5;
w1 = 1e4;
w2 = 1e6;
s = tf('s');
a = a0/(1+s/w1)/(1+s/w2)
A0 = 10;
b = 1 / A0;    % approximation for ab>>1
R1 = 10000;
R2 = R1 * (1/b - 1)
A = feedback(a,b);
K = R1/(R1+R2);
C = [1:.2:3]*1e-12;

hold on
step(A,'r')
hold on
for n=1:length(C)
  b_array=tf([K*R2*C(n) K],[K*R2*C(n) 1]);
  A_array = feedback(a,b_array);
  L_array = a*b_array;
  step(A_array,'b')
  hold on
endfor
###################################################

I tried to create the cell array with cellfun, but, can not seem to get 
the correct shape.

With looping, I created a cell array of transfer functions, but, step() 
does not like it.

###################################################
L_array=A_array=b_array=cell(size(C'));
for idx=1:length(C)
  b_array{idx,1}=tf([K*R2*C(idx) K],[K*R2*C(idx) 1]);
  A_array{idx,1} = feedback(a,b_array{idx,1});
  L_array{idx,1} = a*b_array{idx,1};
endfor;
step(A,'r',A_array,'b');
###################################################

Tom Dean