# Evaluating a function with Matlab

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Danny Guana on 18 May 2022
Commented: Danny Guana on 18 May 2022
Hello friends,
Can anyone help me figure out why I am getting an imaginary number in the following code: I am supposed to get 1.36. I have done the same calculation using my scientific calculator and symbolab and cannot find what the error is in my code.
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KSSV on 18 May 2022
t = 10 ;
f = -((t-16.82)/5.604)^1.576
f = -0.3223 + 1.3241i
The result is clear, you are taking exponent of a negative number.

Stephen23 on 18 May 2022
Edited: Stephen23 on 18 May 2022
"Can anyone help me figure out why I am getting an imaginary number in the following code:"
Because you are taking the power of a negative number.
"I am supposed to get 1.36."
The simple, effiicient, MATLAB approach is to use REALPOW:
t = 10 ;
f = realpow(-((t-16.82)/5.604),1.576)
f = 1.3627
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Danny Guana on 18 May 2022
Many thanks, I understood

### More Answers (1)

Torsten on 18 May 2022
Edited: Torsten on 18 May 2022
Then you have to program it as
t = 10;
f = sign(t-16.82).*abs((t-16.82)/5.604).^1.576
An expression
x^a
for x<0 is complex-valued.
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Danny Guana on 18 May 2022
Thanks a lot Torsten