Error on filter() - Subscript indices must either be positive integers or logicals

I'm trying to use filter() to do a moving average on my data, but I keep getting the error "Subscript indices must either be positive integers or logicals." What's really bothering me is I get the same error when I try running the example on the filter() webpage. Here's the example. It breaks on the y=filter(b,a,x) line.

    t = linspace(-pi,pi,100);
    rng default  %initialize random number generator
    x = sin(t) + 0.25*rand(size(t));

    windowSize = 5; 
    b = (1/windowSize)*ones(1,windowSize);
    b = [1/5 1/5 1/5 1/5 1/5]
    a = 1;

    y = filter(b,a,x);

    plot(t,x)
    hold on
    plot(t,y)
    legend('Input Data','Filtered Data')

[Walter Roberson]

What shows up for

which -all filter

Answer 1

[Jan]

Hi Brian, did you see Walter's comment? Most likely the symbol "filter" was overwritten by a variable. Then the builtin function is "shadowed". If this is your problem:

clear filter

and do not use the name of builtin functions for variables in general.

[Bryan Wilson]

Yes! That's exactly right. I had named another variable 'filter.' Changed the variable name and now it works great.

[Jan]

Then Walter has found the problem 12 hours earlier - thanks!