# MATLAB Convolution

I am designing an IIR notch filter using pole-zero placement method. I am trying to convolve the two zero locations using

b1 = [1 exp(i*pi*filterFreq)];
b2 = [1 exp(-i*pi*filterFreq)];
b3 = conv(b1, b2)


which is producing the output of

b3 =

1.0000    1.5917    1.0000


when instead I need it to be

b =

1.0000   -1.5917    1.0000


I feel like this is just a misunderstanding of the math rather than MATLAB. Any advice appreciated.

Cheers

A zero at $$z = e^{j\theta_1}$$ corresponds to the transfer function $$H_1(z) = 1 - e^{j\theta_1}z^{-1}$$. You have an implicit plus sign (rather than minus) in your vectors b1 and b2.