Function implementation in Matlab [closed]

I want to implement this function $$𝑓[n,m] = a^{n+m}u[n]$$ using 41×41 array, where $$u[n] =1$$ since all the value will be positive, and $$n,m$$ from 0 to 40. But it gives a wrong value.

N=40
M=40
a=0.9
x =zeros(41,41)
for col = 1:41
for row = 1:41
for k=0:N
for i=0:M
x(row,col)=a.^(k+i)*1;
end
end
end
end
• This is not a signal processing question, but a Matlab basic programming question. There's a specific close reason that clarifies that these are off-topic here, but can be asked (if appropriate there) on Stackoverflow.com. May 8 '20 at 13:47

I believe this will do:

x=a.^((0:40)+(0:40)’)
• +1 for the 'expanding vector' Matlab sum (weird as it may seem) May 8 '20 at 15:46
• See this blog post for an interesting discussion on this «implicit expansion» behaviour: blogs.mathworks.com/loren/2016/10/24/… May 16 '20 at 18:03
N=40;
M=40;
a=0.9;
x =zeros(M+1,N+1)
for n = 0:N
for m = 0:M
% add 1 for Matlab's indexing offset
x(n+1,m+1)=a.^(m+n)*1;
end
end

If you want to fix your code as written try this. You have too many loops, you only need two. Knut's code is a lot faster and more efficient though