In variational calculus, the first variation is written as \delta F for some functional F. Vectors are often typeset with boldface, i.e. \vec{x} becomes \mathbf{x}. If I want to typeset the first variation of a vector, would I make the Delta bold as well?

I.e, which is "correct"? \delta \mathbf{x} or \mathbf{\delta x}?

Edit: The functional itself is scalar, but some constituents may not be. Functionals

  • But a vector is not a functional no? Then it needs \delta F[\mathbf{x}]. Or are you considering a scalar product?
    – percusse
    Jan 5 '13 at 13:43
  • 3
    It seems to have nothing to do with (La)TeX. Jan 5 '13 at 15:08

I believe the former to be the correct way. In essence you'd make the \delta a vector itself by typesetting it in bold face, which is clearly wrong. The variation constitutes more of an operator than a vector, in a similar vein with the integral or a differential for example, neither of which should be bold faced, regardless of the type of integrand. The better question in my eyes is, should you format it upright, cf. here

  • Good point with the upright issue.
    – Psirus
    Jan 5 '13 at 13:48

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