\jmathThe \jmath command in LaTeX is used to produce a dotless 'j', which is useful in mathematical notation where the dot of the 'j' might interfere with other symbols, such as in indices or when used with accents.
Dotless 'j' with a hat accent
\hat{\jmath}Dotless 'j' used as a subscript index
\jmath_{i}Dotless 'j' with a vector arrow
\vec{\jmath}