\usepackage{txfonts}
\DeclareMathOperator{\Div}{\text{div}}
\newcommand{\calF}{\mathcal{F}}
\newcommand{\vv}{\mathbf{v}}
\newcommand{\vU}{\mathbf{U}}
\newcommand{\vu}{\mathbf{u}}
\newcommand{\vd}{\mathbf{d}}
\newcommand{\vD}{\mathbf{D}}
\newcommand{\vw}{\mathbf{w}}
\newcommand{\vf}{\mathbf{f}}
\newcommand{\vg}{\mathbf{g}}
\newcommand{\vh}{\mathbf{h}}
\newcommand{\vn}{\mathbf{n}}
\newcommand{\vy}{\mathbf{y}}
\newcommand{\vz}{\mathbf{z}}
\newcommand{\vr}{\mathbf{r}}
\newcommand{\vtau}{\mathbf{\tau}}
\newcommand{\vuobs}{\vu_{\mathrm{obs}}}
\newcommand{\tX}{\mathtt{X}}
\newcommand{\tY}{\mathtt{Y}}
\newcommand{\tU}{\mathtt{U}}
\newcommand{\tw}{\mathtt{w}}
\newcommand{\obs}{\mathrm{obs}}
\newcommand{\reg}{\mathrm{reg}}
\newcommand{\Tik}{\mathrm{Tik}}
\newcommand{\misfit}{\mathrm{misfit}}
\newcommand{\scale}{\mathrm{scale}}
\newcommand{\ra}{\rightarrow}
\def\ip<#1,#2>{\left<#1,#2\right>}