Subscript indices must either be real positive integers or logicals.

Dan (view profile)

on 29 Sep 2013
Latest activity Commented on by azure roy

on 3 Jun 2016

Matt J (view profile)

```%Number of components
K = zeros(1,111);
```
```%sampling frequency/timing interval
fs = 8000;
Fs = 10*fs;
T = 2;
```
```%frequency components
fk =100:30:3400;
```
```%amplitude components
Ak = rand(1,length(K));
```
```%phase components
phik = 2*pi*rand(1,length(K));
```
```for t = 0:(1/Fs):T %time interval
K = Ak.*cos(2*pi.*fk*t + phik);
y = t/(1/Fs)+1;
xt(1,y) = sum(K,2);
end
```

I'm trying to run this code but for some reason there is an error at y = 14 which is no where near the end of the loop. I'm pretty sure that xt(1,14) is a valid index. Any reason why this might be happening?

on 29 Sep 2013
Edited by Matt J

Matt J (view profile)

on 29 Sep 2013

y will not be 14 exactly because you use non-integer arithmetic to generate it. Using round() might be a possible fix.

on 29 Sep 2013
Edited by dpb

dpb (view profile)

on 30 Sep 2013

The answer is in the following--

```>> fs = 8000;
>> Fs = 10*fs;
>> t=0:1/Fs:2;
>> y = t/(1/Fs)+1;
>> all(fix(y)==y)
ans =
0
>> neq=find(fix(y)~=y);
>> neq(1)
ans =
14
>> y(14)-fix(y(14))
ans =
1.7764e-15
>> length(neq)
ans =
39209
>> length(y)
ans =
160001
>>
```

Moral: Don't use FP calculations as indices...

Dan

Dan (view profile)

on 29 Sep 2013

Hmm where does that discrepancy in y values come from?

dpb

on 30 Sep 2013

FP rounding...

Wayne King (view profile)

on 29 Sep 2013
Edited by Wayne King

Wayne King (view profile)

on 29 Sep 2013

I'm not sure what you are trying to do, create a superposition of sine waves with different frequencies and a random phase and amplitudes? If so, I'll show you how to do that.

But your immediate issue here is that y=0 when t = 0 and then you try to access the zero-th column of xt(), but that can't exist.

You can do this.

```Fs = 8000;
t = (0:1/Fs:2-1/Fs)';
```
```fk = 100:30:3400;
X = zeros(length(t),length(fk));
```
```phi = -pi+2*pi*rand(1,length(fk));
```
```Ak = rand(1,length(fk));
```
```tmat = repmat(t,1,length(fk));
omega = 2*pi*fk;
omega = repmat(omega,size(tmat,1),1);
phi = repmat(phi,size(tmat,1),1);
freq_phi = omega.*tmat+phi;
Ak = repmat(Ak,size(tmat,1),1);
sigz = Ak.*cos(freq_phi);
sig = sum(sigz,2);
```

Now plot the resulting signal

```plot(t,sig)
```

azure roy

azure roy (view profile)

on 3 Jun 2016

theta_i(i,j)=2*pi*rand(1) this is showing subscript indices should be integer or logical value. please help with the solution.