Square matrix used in population biology to predict population growth. The top row of the matrix is the fecundity for each age class of mothers, and a subdiagonal is constructed from the number of individuals surviving from age class \(x\) to \(x + 1\). Multiplied by the population vector of the number of female offspring in each age class \(x\) at time \(t\), it predicts the age distribution of the population at the next time step \(t + 1\), corresponding to the age class interval \(x + 1\).