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Degree 1 Gauss–Legendre on a quadrilateral

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In this example:
\(\displaystyle l_{0}:\mathbf{v}\mapsto\displaystyle\int_{R}v\)
where \(R\) is the reference element.

\(\displaystyle \phi_{0} = 1\)

This DOF is associated with face 0 of the reference element.
\(\displaystyle l_{1}:\mathbf{v}\mapsto\displaystyle\int_{R}(\sqrt{3} \cdot \left(2 s_{1} - 1\right))v\)
where \(R\) is the reference element;
and \(s_{0},s_{1}\) is a parametrisation of \(R\).

\(\displaystyle \phi_{1} = \sqrt{3} \cdot \left(2 y - 1\right)\)

This DOF is associated with face 0 of the reference element.
\(\displaystyle l_{2}:\mathbf{v}\mapsto\displaystyle\int_{R}(\sqrt{3} \cdot \left(2 s_{0} - 1\right))v\)
where \(R\) is the reference element;
and \(s_{0},s_{1}\) is a parametrisation of \(R\).

\(\displaystyle \phi_{2} = \sqrt{3} \cdot \left(2 x - 1\right)\)

This DOF is associated with face 0 of the reference element.
\(\displaystyle l_{3}:\mathbf{v}\mapsto\displaystyle\int_{R}(12 s_{0} s_{1} - 6 s_{0} - 6 s_{1} + 3)v\)
where \(R\) is the reference element;
and \(s_{0},s_{1}\) is a parametrisation of \(R\).

\(\displaystyle \phi_{3} = 12 x y - 6 x - 6 y + 3\)

This DOF is associated with face 0 of the reference element.