I want to optimize the below function with GA(genetic algorithm): $$ \min_{l_{x_1},l_{x_2},l_d}||S_QS(z)||_2 $$

$S_Q$ and S(z) are defined as: $$ S_Q=\Biggm[\matrix{6.6549 &-0.806&6.883\cr -0.806 &12.146 &6.818\cr 6.883 &6.818 &29.071}\Biggm] $$ $$ S(z)=\Biggm[\matrix{z-1-l{x_1}&-0.05&-1 \cr -l{x_2}&z-1&-1\cr -l_d &0 &z-1}\Biggm]^{-1} $$ where z is the z-transform variable

I write below code and using optimization toolbox in MATLAB

function z=objective_function(o)
    6.883, 6.818,29.071]

but do not work and give me that error (The "norm" command cannot compute the H2 norm of improper discrete-time models)

  • 1
    $\begingroup$ Hi welcome to engineering. This looks like homework. Please show your efforts to solve this. $\endgroup$ – NMech Mar 11 at 9:46
  • $\begingroup$ I added the code I wrote and this problem relates to my Thesis. I appreciate it if you help me. $\endgroup$ – user212662 Mar 11 at 12:29
  • $\begingroup$ Not an answer, but in matlab it is better to use backslash instead of calculating the inverse separately, so Sq / s instead of Sq*in(s). Is should be faster and more accurate. $\endgroup$ – fibonatic Mar 11 at 13:11
  • $\begingroup$ Your optimization problem also seems to be note well enough defined, since $z$ seems to still be a free variable and thus the objective function can't be evaluated numerically. $\endgroup$ – fibonatic Mar 11 at 13:14

Taking the norm of a system is something different that taking the norm of a matrix. Luckily, matlab has you covered: https://nl.mathworks.com/help/control/ref/lti.norm.html

This page even shows an example in discrete time. However, what I think is missing in your example is that you should provide a sampling time. As the norm is calculated for every value of $z$ (I believe it is something like the integral of the trace of the absolute value of the system for every $e^{jw}$), the sampling time should be included. I'd recommend first testing if z=tf('z', -1); works, but otherwise specify a generic sampling rate.


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