Editing Toom–Cook multiplication (section)

=== Toom-1.5 ===
Toom-1.5 (''k''<sub>''m''</sub> = 2, ''k''<sub>''n''</sub> = 1) is still degenerate: it recursively reduces one input by halving its size, but leaves the other input unchanged, hence we can make it into a multiplication algorithm only if we supply a 1 × ''n'' multiplication algorithm as a base case (whereas the true Toom–Cook algorithm reduces to constant-size base cases). It requires 2 evaluation points, here chosen to be 0 and ∞. Its interpolation matrix is then the identity matrix:

: <math>\left(\begin{matrix}1 & 0 \\ 0 & 1\end{matrix}\right)^{-1} =
\left(\begin{matrix}1 & 0 \\ 0 & 1\end{matrix}\right).</math>

The algorithm is essentially equivalent to a form of long multiplication: both coefficients of one factor are multiplied by the sole coefficient of the other factor.