Sign of imaginary value changes after converting to array

When I calculate these complex numbers, they have positive imaginary components. However, in the complex array z, all of the nonzero imaginary components become negative.

I can't find this behavior in the documentation so I do not understand what is going on.

a = 2 + 1j;
b = 1 + 3j;
% a)
z1 = a*b;

% b)
z2 = b*conj(b);

% c)
z3 = a^3;

% d)
z4 = b/a;

z = [z1; z2; z3; z4];

Answer 1

[Steven Lord]

My guess is that you accidentally used the conjugate transpose operator (') instead of the non-conjugate transpose operator (.') somewhere in your code.

v = (1+1i)*(1:5);
imag(v)

ans = 1×5

1 2 3 4 5

x = v.';
imag(x) % non-conjugate

ans = 5×1

1 2 3 4 5

y = v'; % conjugate
imag(y)

ans = 5×1

-1 -2 -3 -4 -5

[Nicholas Acuna]

That did it thanks! Didn't know about that operator

I originally had z = [z1 z2 z3 z4]'; and when I switched to [z1; z2;...]; I tried clearing and rerunning the script but I was in debug mode so it didn't actually do anything.

Answer 2

[James Tursa]

Here is what I get:

>> a = 2 + 1j;
>> b = 1 + 3j;
>> z1 = a*b
z1 =
  -1.0000 + 7.0000i
>> z2 = b*conj(b)
z2 =
    10
>> z3 = a^3
z3 =
   2.0000 +11.0000i
>> z4 = b/a
z4 =
   1.0000 + 1.0000i
>> z = [z1; z2; z3; z4]
z =
  -1.0000 + 7.0000i
  10.0000 + 0.0000i
   2.0000 +11.0000i
   1.0000 + 1.0000i

Try clearing your workspace and starting from scratch. Maybe you inadvertently used different variables?