Force element access inside for loop

Hello, I'm playing with transfer functions to extract the causal part of one.

However, when I do

z = tf('z',0.001); tfCaus = tf(k0plus, 0.001);  % adding the delta@0
for stbIdx = find(abs(p)<1)
    tfCaus = tfCaus + r(stbIdx)/ (z-p(stbIdx))^(m(stbIdx));
end

I get an error about the ^ (transfer function) operator failing as the inputs are treated as vectors . In particular the error is

In the expression "M^K", the model M must have the same number of inputs and outputs.

while explicitly requesting the index, doing

tfCaus = tfCaus + r(2)/ (z-p(2))^(m(2))

works as expected. It seems to me that stbIdx isn't properly substituted as scalar at runtime. I've checked and and it's a proper vector.

The same behavior fails when doing

zpk([],p(stbIdx)*ones([m(stbIdx),1]), r(stbIdx))

but the code below works

zpk([],p(2)*ones([m(2),1]), r(2))

Answer 1

[Tommy]

Is p a column vector?

Notice the difference between the following:

>> for i = 1:3
    disp('a')
end
a
a
a

and

>> for i = (1:3)'
    disp('a')
end
a

Does it work if you use

for stbIdx = find(abs(p)<1)'

[Massimo Pesavento]

Thank you so much, indeed that's the cause, I didn't know MATLAB treated them differently.

Have a nice day

[Tommy]

Fantastic, same to you