why do i get this error? 'Subscript indices must either be real positive integers or logicals.' thanks for any help!!!

h=0.1;

t=36;

N=(t/h);

t=zeros(1,N+1);

p=zeros(1,N+1);

t(1)=0;

p(1)=87;

for n=1:N

           t(n+1)=t(n)+h;

           u=sin((2*pi*t)/12);

           H=15*[nthroot(u,15)+1]

           p1(n+1)=p(n)+h*[(0.016*p(n)*(100-p(n)))-H(n)];

           p(n+1)=p(n)+(h/2)*[[(0.016*p(n)*(100-p(n)))-H(t)]+[(0.016*p(n+1)*(100-p(n+1)))-H(n+1)]];

end

Answer 1

[Walter Roberson]

Your line

p(n+1)=p(n)+(h/2)*[[(0.016*p(n)*(100-p(n)))-H(t)]+[(0.016*p(n+1)*(100-p(n+1)))-H(n+1)]];

includes the subexpression H(t). H(t) denotes indexing the vector H at the locations designated in t. But t is, at that point, a vector of values that are not integers, so this is going to fail.

In the other places you use H, you use H(n) or H(n+1) which do not have that problem.

Note: in MATLAB, [] designate building matrices or vectors, rather than being parenthesis. There are a number of cases where you would get away with using [] instead of () but it will cause problems eventually.

Answer 2

[Stalin Samuel]

Subscript indices must either be real positive integers or logicals