Btukfyl

$$ = 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?

The immediate problem is solved by replacing the text-mode instruction ~{A} with the math-mode directive tilde{A}.

In addition, you may 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 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 the shapes of the accents can differ between text and math modes. In math mode, 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.

documentclass{article}

usepackage{mathtools} % for "mathclap" macro; loads "amsmath" package

begin{document}   

[

   = sum_{e in A} w(e)

   = sum_{e in A} w(e) + 

     sum_{mathclap{substack{e in {(r,v)} \ text{s.t.}, v in V(G)}}} w(e) 

   = w(tilde{A}) 

]

end{document}

documentclass{article}

usepackage[T1]{fontenc}

usepackage{booktabs,array,lmodern}

newcolumntype{C}{>{$}c<{$}} % automatic-math version of "c" column type

begin{document}

noindent

begin{tabular}{@{} l cc>{itshape}c lCC @{}}

toprule

Accent name & multicolumn{3}{c}{Text mode} 

            & multicolumn{3}{c@{}}{Math mode} \

cmidrule(lr){2-4} cmidrule(l){5-7}

            & how to & multicolumn{2}{c}{result} 

            & how to & multicolumn{2}{c@{}}{result} \

midrule

acute             & verb|'| & 'A & 'A & verb|acute| & acute{mathrm{A}} & acute{A} \

grave             & verb|`| & `A & `A & verb|grave| & grave{mathrm{A}} & grave{A} \

circumflex        & verb|^| & ^A & ^A & verb|hat|   & hat{mathrm{A}}   & hat{A}   \

squiggle, tilde   & verb|~| & ~A & ~A & verb|tilde| & tilde{mathrm{A}} & tilde{A} \

macron, bar       & verb|=| & =A & =A & verb|bar|   & bar{mathrm{A}}   & bar{A}   \

dot accent        & verb|.| & .A & .A & verb|dot|   & dot{mathrm{A}}   & dot{A}   \

diereris (Umlaut) & verb|"| & "A & "A & verb|ddot|  & ddot{mathrm{A}}  & ddot{A}  \

bottomrule

end{tabular}

end{document}

Text accents and math accents have different syntax in LaTeX: to get Ã, you would use ~{A} in textmode, but tilde A or widetilde A (the latter for a wider version) in mathmode.

Here is a table showing how to get different kinds of accents in textmode and mathmode.

Thus, your corrected code is

= sum_{e in A} w(e) = sum_{e in A} w(e)+ sum_{e in {(r,v)| v in V(G)}} w(e) = w( tilde A )

I solved the issue by replacing ~{A} with tilde{A}.

Just use the package lmodern.

documentclass{article}

usepackage{amsmath,amssymb}

usepackage[utf8]{inputenc}

usepackage[T1]{fontenc}

usepackage{verbatim}



usepackage{lmodern}



begin{document}



$$ y = w( ~{A} ) $$



You can also disregard the use of verb=~{A}= and use à directly, like the example below:



$$ y = w( Ã ) $$   



end{document}