surrogate

The cat acted as a surrogate mum to the chicks.

For some people, reading travel books is a surrogate for actual travel.

wives of MPs are looked on as surrogates for their husbands while the latter are at Westminster.

In the 1950s Harlow compared monkeys raised by their mothers with monkeys reared by wire or terrycloth surrogate mothers.

It should be noted that the method for updating multipliers is similar but different to the surrogate subgradient method, which is more robust and stable for accelerating the convergence rate.