# Abs and angle of complex number with symbolic object

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john on 4 Mar 2013
Hi,
If r=sym('a')*exp(j*sym('b')) is a symbolic object, and
1. if I write abs(r), I get abs(a).....I need get only "a" without abs
2. if I write angle(r), I get error
??? Undefined function or method 'atan2' for input arguments of type 'sym'.
Error in ==> angle at 14 p = atan2(imag(h), real(h));
Can you help me please? How can I solve this?

Walter Roberson on 5 Mar 2013
There is no "complex argument" function for symbolic variables exposed at the MATLAB level. You can, though, define
arg = @(V) feval(symengine, 'arg', V);
john on 7 Mar 2013
Did you mean this code
r=sym('a')*exp(j*sym('b'));
arg = @(r) feval(symengine, 'arg', r);
number=arg(r);
????
But I got again error
??? Undefined function or method 'atan2' for input arguments of type 'sym'.
Error in ==> angle at 14 p = atan2(imag(h), real(h));
Btw, what is better to use, atan or atan2 in form "P = 2 * atan( (sqrt(X.^2 + Y.^2) - X) ./ Y )";
Thank you

Brian B on 4 Mar 2013
Edited: Brian B on 4 Mar 2013
Well, for part 1 you have to assume a is a non-negative real:
syms a
assume(a>0)
Then
>> abs(a)
ans =
a
I have not tried the second part, but you can imagine dividing by the magnitude and taking a log....
john on 5 Mar 2013
Tanks, but It doesn't help for angle(r)