simple low pass filter - matlab equivalent

Hi every one.

could anyone tell me a fast matlab equivalent to the following low-pass filter:

clc
clear 
close all

tau = 0.5;
freq = 10;
weight = 2-exp(1./(tau*freq));
samplesize = 30000;

a = [1:samplesize]';
b = rand(samplesize,1).*20+390 + sin(a./10).*10;

%LowPass Filter
lp = NaN(size(a));
lp(1) = b(1);
for i = 2:length(a)
    lp(i)  = lp(i-1).*weight+b(i).*(1-weight);
end

Answer 1

[Star Strider]

It looks like an fir filter. When I analyse it with freqz, it turns out ot be a very strange filter, and almost a comb filter. I have no idea how to approximate it with Signal Processing Toolbox functions (other than perhaps fir1 or related functions) because I have no idea what you want it to do.

Run this to see the filter Bode plot. Change the upper limit in the set call (currently 0.02) to see more of the plot. Change the exponent in 2^15 to change the resolution:

figure(1)
freqz(lp, 1, 2^15)
set(subplot(2,1,1), 'XLim', [0  .02])
set(subplot(2,1,2), 'XLim', [0  .02])