Tests of three DEM codes with Gaussian DEM models. The models include: a single Gaussian model with (a) σ = 0.06, (b) σ = 0.2 , and (c) double-Gaussian DEM model with σ = 0.06. The peak temperatures vary from log₁₀ T = 5.6 to 7.6 (in model c, one Gaussian peaks at a fixed log₁₀ T = 6.3). Top row: DEM solutions for Gaussian models (black) peak at log₁₀ T = 6.2 (7.0 in panel c). The solutions from the regularized inversion are shown in green, the original sparse inversion code in red crosses (the code did not find solutions for all the tests), and the sparse inversion code with new settings in blue. Middle row is the same as top row, but for Gaussian models peak at log₁₀ T = 7.6. Bottom row: comparison of the T_EM derived from the solutions and the models. The dashed lines show the expected relation between peak temperatures and T_EM. The area in gray shows the range of expected values ±σ.