Why is the string below the first conditional not printed?

I need help understanding why the string below the first conditional is not printed when AA, BB, CC are clearly equal. See attachment below

[dpb]

(AA==BB) == 1 && (CC) == 1

is not good syntax.

if AA==1 & BB==1 & CC==1

will work; more succinct forms can be written if you would use arrays for variables instead of indivdually naming the variables (generally a bad practice to use MATLAB efficiently to have mulitple similarly-named/functionally equivalent variables as above).

[Andromeda]

I tried if (AA == BB) == (CC ==1) first and that didn't produce the expected output and thus resorted to what you see above. Why doesn't if (AA == BB) == (CC ==1) work as well?

"if you would use arrays for variables instead of indivdually naming the variables ", care to give me an example?

Answer 1

[Cris LaPierre]

Because the result of the dot products is not exactly 1.

A = [2 2 -1+4i]/5;
B = circshift(A,-1);
C = circshift(B,-1);

AA = dot(A,A)

AA = 1.0000

BB = dot(B,B)

BB = 1.0000

CC = dot(C,C)

CC = 1.0000

% now subtract 1. Result is not 0
AA-1

ans = 2.2204e-16

BB-1

ans = 2.2204e-16

CC-1

ans = 2.2204e-16

[Andromeda]

Well, that is odd. For a vector to form an orthonormal basis[algebra], the dot product of the vector with itself should be equal to 1

[dpb]

Floating point arithmetic is only an approximation to algebra...see <Goldberg - What Every Computer Scientist Should Know> for detailed explanation. There are some other discussions and examples in the documentation as well.