Abs and angle of complex number with symbolic object
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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?
采纳的回答
Walter Roberson
2013-3-5
There is no "complex argument" function for symbolic variables exposed at the MATLAB level. You can, though, define
arg = @(V) feval(symengine, 'arg', V);
3 个评论
john
2013-3-5
Walter Roberson
2013-3-5
After the definition above, you would use
arg(r)
john
2013-3-7
更多回答（1 个）
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....
6 个评论
Brian B
2013-3-4
You may also have to
assume(b,'real')
john
2013-3-4
编辑：Walter Roberson
2013-3-4
Brian B
2013-3-4
What version of the Symbolic Math Toolbox do you have?
ver('symbolic')
john
2013-3-4
Try
a = sym('a','positive')
b = sym('b','real')
That works for me in R2011b, including computing the magnitude of r. I don't see a good way to get the argument, though.
john
2013-3-5
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