# Tagged Questions

Question on the meaning, history, and usage of mathematical symbols and notation. Please remember to mention where (book, paper, webpage, etc.) you encountered any mathematical notation you are asking about.

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### Tensor notation about $A^Tx$

I can express $x=x^ie_i$ and $x^T$ by $x_ie^i$. But how to express $A^Tx$ where $A=a^i_je_i\otimes e^j$? I don't think I can write as $a^j_ix^i$ or $a^j_ix^j$.
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### Proper way to use universal quantification with multiple arguments

Which one is correct? $\forall x \in X, y \in Y:$ some expression or $\forall x \in X \wedge y \in Y:$ some expression or $\forall x \in X \forall y \in Y:$ some expression
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### What does the notation $P[X\in dx]$ mean?

I am studying probability, specifically regular conditional distributions, and came across the notation $P[X\in dx]$. What does this mean? Here, $X$ is a random variable and $P$ is a probability ...
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### Notation and terminology for functions, interpreting $f(y)$

It seems to me there are two different interpretations of a symbol $f(y)$. I will explain what I mean: Suppose I have a function $f(x) = x$. (I took the identity map to have a simple example). Also ...
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### What does power of '+' in $\hat{\beta}_j=\operatorname {sign} (\hat{\beta^0_j})(|\hat{\beta^0_j}|-\gamma)^+$means?

I encountered the following equation in a paper. $$\hat{\beta}_j=\operatorname {sign} (\hat{\beta^0_j})(|\hat{\beta^0_j}|-\gamma)^+$$ What does the power of '+' mean? The paper can be viewed at: http:...
### Question about Notation. What does this means? $f[0]=1, f[0,1]=-1$
Question about Notation. What does this means? $f[0]=1, f[0,1]=-1, f[0,1,2]=2$ (The values are exact, which is pretty confusing too, if they are refering to intervals) This question is from a ...