What is wrong with my MATLAB code? Can someone check it for me..? (Sum of series)

I have a problem with MATLAB coding. I'm trying to find the solution for the fractional-order equation. I already found for c0 until c3. Then I want to find sum of series as follow, and m=0,1,...,4. But I got error that said 'Index exceeds matrix dimensions'. Why this happened? And how to fix my code? I hope someone can help me.

clear;

syms x t D n h q

% Parameters needed to solve the equation
p = 0.012;  % Proliferation rate (per day)
x0 = 25;    % The middle of considered interval (mm)
epsilon = 0.01; % suggest by Ozugurlu
cmax = 62.5;    % Carrying capacity of GBM tumour cells
alpha = 1.0;    % Fractional derivative order
s = 0;
r = 1;

for m=2:3
    
    c(1) = (1/((sqrt(2*pi()))*epsilon))*exp((-1/2)*(((x-x0)/epsilon)^2));   % Initial concentration (c0)
    c(2) = (D/((sqrt(2*pi()))*(epsilon^3))-(D*((x0-x)^2))/((sqrt(2*pi()))*(epsilon^5))-p/((sqrt(2*pi()))*epsilon))*(h*((t^alpha)/(gamma(alpha+1))))*exp((-1/2)*(((x-x0)/epsilon)^2))+((h*p*(t^alpha))/(cmax*2*pi()*(epsilon^2)*(gamma(alpha+1))))*exp((((x-x0)/epsilon)^2));    % c1
 
    d = diff(c(m),x,2);
    c(m+1) = (n+h)*c(m)-(h*(t^alpha)/(gamma(alpha+1)))*(D*d+p*c(m)-(p/cmax)*((c(m))^2))
    
    while r<=m
        c = c(r)*(q^(r-1))+s;
        s = c;
        r = r+1;
    end
 
    
end
disp('sum of series=')
disp(s)

Answer 1

[Walter Roberson]

inside the while loop you calculate something making use of c indexed at a value. you then store that on top of all of c, making c a scalar. Next time through the loop you try to index c but c is a scalar now.