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# Why am I getting this error "??? error using ==> times matrix dimensions must agree" in matlab?

Asked by Debajyoti on 21 Apr 2013

design a FIR low pass filter using Kaiser window

```a1phap=0.1
```
```a1phas=44
```
```ws=30
```
```wp=20
```
```wsf=100
```
```B=ws-wp
```
```wc=0.5*(ws+wp)
```
```wcr=wc*2*pi/wsf
```
```D=(a1phas-7.95)/14.36
```
```N=ceil((wsf*D/B)+1)
```
```a1pha=(N-1)/2
```
```gamma=(.5842*(a1phas-21).^(0.4)+0.07886*(a1phas-21))
```
```n=0:1:N-1
```
```hd=sin(wcr*(n-a1pha))./(pi*(n-a1pha))
```
```hd(a1pha+1)=0.5
```
```wk=(kaiser(N,gamma))
```
```hn=hd.*wk     % *(HERE I AM GETTING THIS ERROR)*
```
```W=85:5:120
```
```h=freqz(hn,1,W)
```
```plot(W/pi,20*log10(abs(h)))
```

those two matrices have the same dimensions of 27..still why this error?

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Answer by Cedric Wannaz on 21 Apr 2013

You have to transpose either wk or hd, because one is a column vector and the other a row vector. E.g.

` hn = hd .* wk.'`

Answer by the cyclist on 21 Apr 2013
Edited by the cyclist on 21 Apr 2013

I don't have the Signal Processing Toolbox, so I can't execute the kaiser() function. However, the documentation indicates that it will output a column vector. Your vector hd is a row vector, so it does not actually have the same dimension. You need to transpose one of them.

Answer by Chandra Shekhar on 21 Apr 2013
Edited by Chandra Shekhar on 21 Apr 2013

Don't use dot product,edit that line like this

hn=hd*wk;

but you will get single value after multiplying,but 'freqz' function requires vector as a input.

if you need vector then do like this, you will get waveform.

hn=hd. * wk ' ;