Results of the calculation of the gradient field G and the application of the LITMUS test. The first row shows estimates for the absolute values of the field G. Panel a) shows G as calculated directly from the posterior mean m of the signal field, whereas panel b) takes into account large-scale uncertainty corrections as described in Sect. 3.2.3. Panel c) shows the absolute value of the polarized intensity P as measured by the WMAP satellite and panel d) shows the result of the LITMUS test, namely Re⁽GP^∗), in arbitrary units, using G and P as shown in panels b) and c), respectively. Note the logarithmic color code of panels a)–c).