Relationship between the nonthermal line width (σ_NT) and gas kinetic temperature, as determined from the H₂CO line ratio, is examined in those parts of the DR21 filament, which are characterized by a Mach number 𝓜≳ 3.0 (see Sect. 4.3.3). A linear fit is applied to the H₂CO 3₀₃−2₀₂ and the combined H₂CO 3_22-2₂₁ and 3₂₁−2₂₀ lines, yielding the following results: log T_kin = (0.42 ± 0.04) × logσ_NT + (1.60 ± 0.01) and log T_kin = (0.41 ± 0.03) × log σ_NT + (1.63 ± 0.01), respectively. In this fitting, the linear fit was performed on the unweighted data using the least squares method. The Pearson correlation coefficients, R, for these fits (red lines) are 0.45 and 0.55, respectively.