The paper describes an automatic inversion code to recover microstructured magnetic atmospheres (MISMAs) by Ðtting Stokes proÐles. These solar model atmospheres incorporate small-scale Ñuctuations of the magnetic Ðeld vector, the velocity, the temperature, etc., which seems to be an intrinsic property of the magnetic photosphere. The model MISMAs considered for inversion have several distinct components. Each one of them is made of slender Ñux tubes, so that the whole vertical stratiÐcation of

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... he MISMA is reconstructed from a Ðnite set of parameters. The inversion code has been thoroughly tested using both synthetic and real observations. In particular, it successfully reproduces line proÐles and model atmospheres corresponding to the quiet Sun and plage regions. As a by-product, we introduce a new error estimate for nonlinear least-squares minimizations.