# inner matrix must agree using *

1 view (last 30 days)
Nicholas Jacobs on 23 Oct 2015
Commented: Star Strider on 23 Oct 2015
when attempting to execute this code I get the following error, can anyone tell me why and how to resolve it, thanks
A= poly(1j*wc*exp((1j*pi)/((2*k)*(2*k-1))))
Error using * Inner matrix dimensions must agree.
Error in Lab_03 (line 29) A= poly(1j.*wc.*exp((1j.*pi)./((2.*k)*(2.*k-1))))

Star Strider on 23 Oct 2015
The poly function wants a vector of roots from which to create a polynomial. I have no idea what the sizes of your arguments (variables) are, so assuming they are all otherwise compatible, (have the same numbers of elements), vectorising the assignment seems the logical direction to go (assuming also that 1j indicates the imaginary operator):
A = poly(1j*wc.*exp((1j*pi)./((2*k).*(2*k-1))))
Nicholas Jacobs on 23 Oct 2015
right on brother, what you said did the trick. Thanks. Why do I need not use the dot operator at the other locations like I had before or like the guy above me wrote? Thanks again
Star Strider on 23 Oct 2015
My pleasure.
The dot operator specifies element-wise operations as opposed to conventional matrix operations. MATLAB defaults to matrix operations, so you have to specify element-wise operations. See the documentation for Array vs. Matrix Operations for a full description. (A useful function in dealing with arrays is bsxfun. I don’t know if you need it here, but it’s good to know about.)

Eng. Fredius Magige on 23 Oct 2015
Hi, it might be
A= poly(1j.*wc.*exp((1j.*pi)./((2.*k)*(2.*k-1))))
Nicholas Jacobs on 23 Oct 2015
thanks for the input brother.