What changes should I make to save the values of P? P should at least be a 2×2 matrix!!

this is the code:

 for k=1:10

    n=2*k-1

    a1=sin((n*pi.*x)/b);

    a2=sinh(n*pi.*y/b);

    a3=n*sinh(n*pi*a/b);

    sum=sum+c.*a1.*a2/a3;

    P=[n, sum]

 end

Answer 1

[Andrei Bobrov]

n = (1:2:19)';
t = n*pi/b;
P = [n, cumsum(c*sin(t*x).*sinh(t*y)./sinh(t*a)./n)];

Answer 2

[Walter Roberson]

P(k,:) = [n, sum];

Note: do not name a variable "sum", as that interferes with the key MATLAB routine "sum"