Trying to do central difference using for loop, getting error

m=1;
k=1;
c=1;
x(2)=0;
dx=1;
d2x=-1;
h=0.5;

for i=2:0.1:20
    x(i-1)=x(i)-h*dx+(h/2)*d2x;
    x(i+1)=(1/(m/h^2)+(c/2*h))*((2*m/h^2-k).*x(i)+(c/2*h-m/h^2).*x(i-1));

end
plot(x)

what is wrong with my code, I am getting an error Subscript indices must either be real positive integers or logicals. As you can see I am trying to get a plot of x(i+1) which depends on x(i) and x(i-1), thanks

appreciate all the help

[Jan]

I've formatzted your code using the "{} Code" button. You can do this by your own also.

Answer 1

[David Barry]

You must index into an array/matrix with integer values. In your case you are trying to index into variable x with the variable i but you have asked for i to range from 2 to 20 in 0.1 steps. What are you expecting x(2.1) to give for example?

[Ismail khalil]

I have done this and got an a run indeed, but the answer was very different in value than I expected, but I guess you solved my error, thanks