```
$$ = \sum_{e \in A} w(e)
= \sum_{e \in A} w(e)+ \sum_{e \in \{(r,v)| v \in V(G)\}} w(e)
= w( \~{A} ) $$
```

I get the following error message:

Error: Please use \mathaccent for accents in math mode for the following code

I'm not sure what's wrong with it. I'm in math mode by using `$$ $$`

, am I not?

## Best Answer

The immediate problem is solved by replacing the text-mode instruction

`\~{A}`

with the math-mode directive`\tilde{A}`

.You may also want to make the equation both more compact and more readable by (a) introducing a line break in the material set below the third

`\sum`

symbol (via a`\substack`

instruction) and (b) eliminating the whitespace that's otherwise inserted to the left and right of that summation symbol (via a`\mathclap`

instruction).Addendum: For the sake of completeness/reference, here's a list of common accents and how they should be produced in text and math mode, respectively. Note that the positions and, in the case of text-upright versus text-italic font shapes, even theshapesof the accents can differ between text and math modes. In math mode, in contrast, the shapes of the math-accent characters are the same regardless of whether`\mathrm`

("math roman") or`\mathit`

("math italics" -- the default) is in effect.