MATLAB: Force element access inside for loop

for loopMATLABtransfer function

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))

Best Answer

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)'
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