Error in a code of Won Young Yang's book

Hi everybody I've got an error during running one Matlab code

would you please tell me what should I do to run it? Code is:

     function [u,x,t] = heat_exp(a,xf,T,it0,bx0,bxf,M,N)
%solve a u_xx = u_t for 0 <= x <= xf, 0 <= t <= T
% Initial Condition: u(x,0) = it0(x)
% Boundary Condition: u(0,t) = bx0(t), u(xf,t) = bxf(t)
% M = # of subintervals along x axis
% N = # of subintervals along t axis
dx = xf/M; x = [0:M]’*dx;
dt = T/N; t = [0:N]*dt;
for i = 1:M + 1, u(i,1) = it0(x(i)); end
for n = 1:N + 1, u([1 M + 1],n) = [bx0(t(n)); bxf(t(n))]; end
r = a*dt/dx/dx, r1 = 1 - 2*r;
for k = 1:N
for i = 2:M
u(i,k+1) = r*(u(i + 1,k) + u(i-1,k)) + r1*u(i,k);
end
end

[Walter Roberson]

What error are you observing?

[Image Analyst]

And how can we reproduce it? In other words, what values of a,xf,T,it0,bx0,bxf,M,N did you pass into it, so that we can run it? Please give code to make those variables with the values you want.

Answer 1

[Walter Roberson]

You have

x = [0:M]*dx

so your x starts at 0.

You then have

it0(x)=sin (pi*x)

so you are trying to assign into it0(0) but 0 is not a positive integer. Just use

it0 = sin(pi*x);

However, your next line is

u(x,0) = it0(x)

with subscript 0, and 0 is not a positive integer.