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I have a continuous variable whose range is within $[-1, 1]$. I want to map the values of this variable to the range $[0, 1]$ instead. What I do is I add the value of $1$ to the the variable and divide the result by $2$`.

To me, this looks like a linear, valid and invertible operation meaning that the mapping is one-to-one between the domain and the co-domain of this operation/function.

I wonder, is my intuition correct? I would appreciate if someone can clarify this.

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  • $\begingroup$ See the MathJax reference for tips on editing mathematical formulae/content. $\endgroup$
    – user0
    Oct 31, 2018 at 14:45
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    $\begingroup$ Technically the function is affine rather than linear. $\endgroup$
    – Matt
    Oct 31, 2018 at 14:46
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    $\begingroup$ @Matt To be fair, the term "linear", in the context of continuous functions of a single variable, can instead refer to those functions of the form $f\left(x\right) = ax + b$. However, since the OP called it a "linear operation", I agree that this frames it in such a way that it should indeed be called affine. $\endgroup$ Oct 31, 2018 at 15:13

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Yes, your intuition is correct. To be precise, you are describing the function $$f: [-1,1] \rightarrow [0,1],$$ $$f\left(x\right) = \frac{x+1}{2},$$ which is bijective and has inverse $$g: [0,1] \rightarrow [-1,1],$$ $$g\left(y\right) = 2y-1.$$

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  • $\begingroup$ Both your answer and C. Grant's answer are satisfactory for me. However, I want the other person to gain the privilege of commenting so I marked his answer as the final answer :) I Hope you don't mind $\endgroup$
    – Amir
    Oct 31, 2018 at 14:51
  • $\begingroup$ Ah, that's nice of you! Yes, I'm happy for you to spread the reps. I was initially a bit suspicious of their answer being so similar to mine, even in the wording, but I think that's just because there's a pretty canonical response here that we've both used, and their reasoning for the inverse is different, so fair enough. $\endgroup$ Oct 31, 2018 at 14:57
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Yes your intuition is correct, in more detail what you've done is defined a one-to-one and onto function $f: [-1,1] \to [0,1] $ where $f(x) =\frac{x+1}{2}$.

If you want to check that is in Infact invertible you can try solving the equation $ x=\frac{y+1}{2} $ where $x$ is the original input, and y is the output of the function $f(x)$

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