on a semiclassical or WKB approximation applied upon the Martin-Siggia-Rose generating functional [@fogedby]. Its main advantage is that it does not involve expansions around classical noiseless solutions, but around classical (extremal) noisy solutions. It would be very interesting to extend these ideas to KPZ problems in the presence walls, namely, to the multiplicative noise universality classes MN1 and MN2.

Numerical results
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Owing to the failure of standard (non-trivial) mean-field approaches and lacking so far of an alternative analytical route, numerical methods are required to glean insight into the system properties. We have carried out simulations of two surface growth models. Both of them, in the absence of walls, are known to belong to the KPZ universality class. An extra rule is then added to generate a bounding wall, as described above.

Model 1
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Our first model was introduced in [@krugs] and is defined as follows: the surface position at time $t$ above a site $x$ on a one-dimensional lattice of size $L$ is given by a continuous height variable $h_t(x)$. A new height configuration is then generated in a three-step process.

1.  Each lattice site $h_t(x)$ is updated according to $h'_t(x)=h_t(x)+a+\eta_t(x)$. $\eta_t(x)$ is a random number uniformly distributed 