Index must be a positive integer or logical

I am getting the following error while running the code:

Attempted to access r(8.5); index must be a positive integer or logical.

Error in L158 (line 15) A(1,1)=r(n+0.5)/(h^2)+r(n-0.5)/(h^2)+a*r(n)

This is the line of code:

h=0.2

n=1.8/h -1

a=1

c=0.25

r=linspace(0.2+h,2,n+1)

A=zeros(n+1,n+1)

b=zeros(n+1,2)

A(1,1)=r(n+0.5)/(h^2)+r(n-0.5)/(h^2)+a*r(n)

Can someone help me with this?

Answer 1

[Mischa Kim]

Sebastiaan, the problem is that in

 A(1,1) = r(n+0.5)/(h^2)+r(n-0.5)/(h^2)+a*r(n)

you are trying to access

 r(8.5)  % n = 8

Array indices need to be integers (or logicals, as pointed out in the error msg), so you could use:

 A(1,1) = r(n+1)/(h^2)+r(n-1)/(h^2)+a*r(n)

provided it does what you need it to do.