Error: Array indices must be positive integers or logical values.

I have looked at past threads and cannot find the issue of my problem. The error is in the last line with description "Array indices must be positive integers or logical values"

q=10; % W/m^3

km=100; %W/Km

kw=500; %W/Km

R1=1;

R2=1.2;

N=5;

Tr=300;

dr=R1/(N+1);

M=zeros(N+N,N+N);

M(N+1,N+1)=-km/((N+1)*dr^2)-kw((N+1)*dr^2);

Answer 1

[Stephan]

the expression

kw((N+1)*dr^2)

is the problem. I suspect a missing * or / - for example:

kw*((N+1)*dr^2)

[Brooke Mitchell]

Thank you so much! After staring at it for hours I completely didn't notice!