How to determine if angles match

I am trying to write code to determine when two precession angles match. Matlab keeps skipping to the last else statement regardless of which elseif statement should be taking precedence.

prec1 = rad2deg(acos(C21./sin(deg2rad(nutation))));

Unrecognized function or variable 'C21'.

prec2 = rad2deg(asin(C31./sin(deg2rad(nutation))));
if abs(prec1 - prec2) < 10^-3
    prec = prec1;
elseif abs(prec1 - (180 - prec2))< 10^-3
    prec = prec1;
elseif abs((360 - prec1) - prec2) < 10^-3
    prec = prec2;
else 
    prec = 360 - prec1;
end

[Image Analyst]

That's not what happens when we run your code. We get that C21 is not defined. What is prec1 and prec2, or what is C21, C31, and nutation?

[Adam Danz]

We can't follow the logic without knowing C21, C31, and while we're at it, nutation.

[Madeleine]

C21, C23, and nutation are arrays that contain ten values calculated earlier in the code.

C12 and C23 are elements of a direction cosine matrix for a two body 1-3-1 rotation sequence and nutation is the angle about body fixed axis u1. precession is the angle about body fixed axis u3.

[Madeleine]

C12 =

0

0.5207

-0.2255

0.6599

0.0813

0.4857

-0.0558

-0.3070

-0.2298

-0.7950

C23 =

0

0.4887

0.0624

-0.3257

0.0516

-0.7995

0.3638

-0.7010

0.2401

-0.6821

nutation =

0

116.6697

53.6137

79.6703

102.4619

32.9411

127.0446

18.0036

103.4862

69.9394

Answer 1

[Walter Roberson]

You would get that behavior if prec1 or prec2 are non-scalar and it does not happen that all of the values pass the tests.

[Madeleine]

How do i make my variables scalar. I tried using ANY and ALL functions but it I still get a non-scalar error