How to assign values with a smooth trend

Hello all

I have a 1by500 array which i have divided into two parts right in the middle (250). Initially its all zeros but i am intending to assign nonzero values in there. The values would look something like this -

N = 500; x = zeros(1,N); d = 25; x(1:N/2-d) = 100; % from 1 to 225 x(N/2+d+1:end) = 10; % from 276 to 500

The problem is that i need the values in between (from 226 to 275) to change smoothly from 100 to 10. The change cannot be linear. I would want a smooth exponential like change and I dont know how i can do that. Can anyone please help me?

Thanks in advance.

Sazzad