conv & filter function in matlab?

[david753]

In matlab, there are two functions that can represent convolution function.
one is CONV, the other is FILTER.
But, their output point numbers are different.
As bellowing example, stp_rep2 is twice times length than stp_rep3.
Which one is more reasonable?

stp_rep1=filter(b,a,x_imp);
stp_rep2=conv(x_in,stp_rep1);
stp_rep3=filter(b,a,x_in);

 

[zorro]

Hi David,

conv(x,b) performs the complete convolution. The length of the result is length(x)+ length(b)-1 .
filter(b,[1],x) gives an output of the same length than x. It doesn’t flush the delay line of the filter.

Assume x is a row vector. Make x0 = [x zeros(1,length(b)-1)]; now filter(b,[1],x0) is the same than conv(x,b) . This is because the additional 0’s are used to flush te delay line.

Which one is more reasonable? It depends of what you need!
Regards

Z

 

[the_jackal]

zorro has provided a good explaination. But if you really need more help while working in the matlab command window type the commands 'help conv' or 'help filter' to see matlab's version.