Looping over a vector with non-integer values

I'm trying to loop through each element of the vector 'N' but it keeps giving me back the 'attempting to access; index must be a positive integer or logical.' Is there a way I can do this without having to do each of them separately?

    N = [15.66 9.27 6.72 4.84 4.1 3.4];
    km_factors = zeros(size(N));
    r = (616/2)/1000; 
    m = 1140;
    vh = 1.999;

    for i = N
        x(i) = (0.3*i)/r;
        z = m/vh;
        km_factors = (2.73e-02*(x(i)))+(9.85e-04*(x(i)^2))-(5.71e-05*(z)) ...
                    +(8.22e-08*(z^2))-(2.87e-05*(x(i)*z));
    end

    disp(km_factors);

[per isakson]

"do each of them separately?" &nbsp What do you mean? Do what separately?

[Levi Autrey]

I guess I should have worded that a little better. I mean loop through each individual number in 'N' 'by hand', if you will.

Answer 1

[Star Strider]

I don’t know exactly what you want, but one solution is to set the for loop index to go from 1 to the length of ‘N’. I substituted ‘N(i)’ for ‘i’ in the ‘x’ assignment, and subscripted ‘km_factors’. It works. Check to be certain it calculates what you want:

N = [15.66 9.27 6.72 4.84 4.1 3.4];
km_factors = zeros(size(N));
r = (616/2)/1000; 
m = 1140;
vh = 1.999;

for i = 1:length(N)
    x(i) = (0.3*N(i))/r;
    z = m/vh;
    km_factors(i) = (2.73e-02*(x(i)))+(9.85e-04*(x(i)^2))-(5.71e-05*(z))+(8.22e-08*(z^2))-(2.87e-05*(x(i)*z));
end

Note that it’s generally not a good idea to use ‘i’ and ‘j’ as variables, including loop counters, because MATLAB uses those for its imaginary operators. Not using them as variables avoids confusion.

[Levi Autrey]

It works. Thank you very much, I've been struggling with this for quite some time.

[Star Strider]

My pleasure!

I remember encountering the same problem when I was learning MATLAB.