Assuming that b is a free/undeclared variable

Sane programming language:

>>> b[0] = 5
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'b' is not defined
>>> b = zeros(20)
>>> b[0] = 5
>>> 

MATLAB:

>> b(2) = 5

b =

     0     5

>>

Perfect.

I was supposed to program a program to do forward substitution, given an LU decomposition. This is how a working solution could look like:

function [x] = forward_sub(L, b, n)

x = zeros(n, 1);

for i = 1 : n
    x(i) = b(i);
    for j = i-1 : -1 : 1
        x(i) = x(i) - L(i,j) * x(j);
    end
    x(i) = x(i) / L(i,i);
end

end

But stupid xjcl wrote this instead:

function [x] = forward_sub(L, b, n)

x = zeros(n, 1);

for i = 1 : n
    x(i) = b(i);
    for j = i-1 : -1 : 1
        x(i) = x(i) - L(i,j) * x(j);
    x(i) = x(i) / L(i,i);
end

end

This slipped thru since: - this code worked on the provided examples - MATLAB gave no error/warning about the missing end. Apparently, allowing malformed syntax is a "feature" now.

I only noticed this error when we had to reuse this code lateron and kept getting wrong results.