Why is MATLAB giving false output for A and B being equal?

[stihl29]

i have this code

A = [2 -2;-2 -1];
A=orth(A);
B=inv(A);
if A==B
disp('match');
else
disp('no match');
end

they are the same, but i always get the output 'no match'

any ideas?

 

[mikeph]

Technically A is not equal to B because the inverse algorithm gives only an approximation.

To see this,

>> orth([2 -2;-2 -1]) - inv(orth([2 -2;-2 -1]))
ans =
  1.0e-015 *
   0.888178419700125  -0.444089209850063
  -0.388578058618805  -0.777156117237609

So your expression is being analysed as false.