Adding boundary conditions to a function

How could I change this function to input the boundry conditions q and g that say u(0,j)=0 (q) and u(1,j)=t (g)?

function u = Heat1DFD_gen(t,x,u0,alpha,q,g)

%

% Heat1DFD numerically solves the one-dimensional heat equation, with zero

% boundary conditions, using the finite-difference method

% u = Heat1DFD(t,x,u0,alpha), where

% t is the row vector of times,

% x is the row vector of x positions,

% u0 is the row vector of initial temperatures at the x positions,

% alpha is a given parameter of the heat equation,

% u is the approximate solution at the mesh points.

%

u = u0(:); % u must be a column vector

k = t(2)-t(1); h = x(2)-x(1); r = (alpha/h)^2*k;

if r > 0.5,

warning('Method is unstable and divergent. Results will be inaccurate.')

end

i = 2:length(x)-1;

j = 1:length(t)-1,

for j = 1:length(t)-1,

u(i,j+1) = (1-2*r)*u(i,j) + r*(u(i-1,j)+u(i+1,j));

end

u = flipud(u');