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I'm looking for the name of the function $f\left(\begin{bmatrix}a & b\\c & d\end{bmatrix}\right)=ad+cb$

which I had encountered a long ago on the internet. It is the same as determinant, except that (in Laplace Expansion) even numbered rows/columns don't have the negative sign. I looked at many webpages about matrix operations, but this one wasn't in any of the lists. Maybe it's because it's used rarely?

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It is called the permanent of the matrix $A$, see wikipedia. We have $$ {\rm perm}(A)=ad+bc. $$

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