# Index in position 1 is invalid. Array indices must be positive integers or logical values. Error in pid_optimized1 (line 17) solution(K,:) = [K a m ts];

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polycarp onyebuchi il 10 Giu 2019
Hi all
I am trying to run this code but I am getting an error 'Index in position 1 is invalid. Array indices must be positive integers or logical values.
Error in pid_optimized1 (line 17)
solution(K,:) = [K a m ts];'
Can someone help me to run this code.
The code is given by
clear all
clc
%Required to optimize a plant with a transfer function 4/s^3+6s^2+8s+4 with
%a PID controller whose transfer function is given by K(s+a)^2/s.
t = 0:0.01:8;
K = 0;
for K =3:0.2:5
for a =0.1:0.1:3
num =[4*K 8*K*a 4*K*a^2];
den = [1 6 8+4*K 4+8*K*a 4*K*a^2];
y = step(num,den,t);
s = 801;while y(s)>0.98&&y(s)<1.02;s = s-1;end
ts = (s-1)*0.01;%ts = settling time;
m = max(y);
if m<1.15 && m>1.10; if ts<3.00
K = K+1;
solution(K,:) = [K a m ts]; %this sorts the solution of K a m ts in a column array
end
end
end
end
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### Risposta accettata

Alex Mcaulley il 10 Giu 2019
You are using K as a logical indexer, but K take non positive integers values, throwing, then, an error. I gues that the solution is:
t = 0:0.01:8;
k = 0;
for K =3:0.2:5
for a = 0.1:0.1:3
num = [4*K 8*K*a 4*K*a^2];
den = [1 6 8+4*K 4+8*K*a 4*K*a^2];
y = step(num,den,t);
s = 801;while y(s)>0.98&&y(s)<1.02;s = s-1;end
ts = (s-1)*0.01;%ts = settling time;
m = max(y);
if m < 1.15 && m > 1.10
if ts<3.00
k = k + 1;
solution(k,:) = [K a m ts]; %this sorts the solution of K a m ts in a column array
end
end
end
end
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Bob Thompson il 10 Giu 2019
Did you make the adjustment he suggested? I copied your code in, changed it to be like Alex has posted and it ran fine for me.
polycarp onyebuchi il 10 Giu 2019
thanks. it is working perfectly.hoping for more help from you guys

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### Più risposte (2)

Bob Thompson il 10 Giu 2019
Modificato: Bob Thompson il 10 Giu 2019
You are recieving the error because you are trying to use K as an index value, but K is not always a positive integer.
for K =3:0.2:5
solution(K,:) = [K a m ts];
Values of K include 3, 3.2, 3.4, 3.6, ...
Matlab cannot define an element as being in position 3.2, or any other value which isn't a positive integer.
As a side note, you should really not change the value of yoru loop index within the loop itself. It is generally considered bad practice, and is very prone to errors.
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polycarp onyebuchi il 10 Giu 2019
please, what is then the solution. thanks

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polycarp onyebuchi il 10 Giu 2019
The error still persist. someone help please
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