Array indices must be positive integers or logical values.

I am trying to make a step model for my peristaltic pump, but in line 6 i get the error: 'Array indices must be positive integers or logical values.'. I have looked it up and it says that that means that there is a variable created in my workspace that overshadows a function. But I have no idea what that means.

n = 0
x = [0:1:60]
m = length(x)
td = 5

while n<=m
    if x(n) == 0
        h(n) = 0
        n = n+1;
    elseif rem(x(n), 2*td) ==0
        h(n) = h(n-1)+0
        n = n+1;
    elseif rem(x(n), 2*td) ~=0
        h(n) = h(n-1)+l
        n = n+1;
    end
end

[Jan]

h(n) = h(n-1)+l ends with a lowercase L. Should this be a one?

Answer 1

[Jan]

The problem is exactly what the error message says (and not a variable shadowing a built-in function):

n = 0
...
while n <= m
    if x(n) == 0

Now you try to access x(0), but indices start at 1 in Matlab. 0 is not "a positive integer". Maybe all you want is to start with

n = 1;

A for loop might be simpler:

x  = 0:60;  % No [] needed: 0:60 is the vector already
td = 5;
h  = zeros(1, length(x));  % Pre-allocate
for n = 1:length(x)
    if x(n) == 0
        % h(n) = 0;  % Is initialized as 0 already
    elseif rem(x(n), 2*td) == 0
        h(n) = h(n-1);  % "+0" is a waste of reading and processing time
    else % No other possibility than:  if rem(x(n), 2*td) ~=0
        h(n) = h(n-1) + 1;  % It was: "+ l", lowercase L - is this wanted?!
    end
end

Or simpler:

x  = 0:60;
td = 5;
h  = cumsum(rem(x, 2 * td) ~= 0);