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--- public:user_software:documentation:makesourcedb [2022-10-21 07:51] – [Format string] Tammo Jan Dijkema
+++ public:user_software:documentation:makesourcedb [2022-10-21 14:25] (current) – Fix non logarithmic si definition Tammo Jan Dijkema
@@ Line 97: / Line 97: @@
 |VShapelet|string| | |Idem for V flux.|
 |SpectralIndex|doubles| |[]|Spectral index. Multiple values can be given enclosed in square brackets and separated by commas. The n-th value defines the n-th order term. \\ Note that the old way of specifying the spectral index (using SpectralIndexDegree and SpectralIndex:i) is not supported anymore. If used, an error is given.|
+|LogarithmicSI|bool| true |Determines the meaning of the spectral index. See Logarithmic SI below|
 |ReferenceFrequency|double|Hz| |Reference frequency (in Hz) for the spectral index|
 |RotationMeasure|double|rad/m<nowiki>^</nowiki>2| |Rotation measure for the polarized flux Q and U|
@@ Line 116: / Line 117: @@
 Note that the polarized flux can be given directly (as Q and U) or by means of the rotation measure, polarization angle, and polarized fraction. An error is given if both are given for the same source.
+=== Logarithmic Spectral Index ===
+If ''LogarithmicSI'' is ''true'' (the default), the source intensity 'I' is computed as
+''I = I0 * (v/v0) ^ (c0 + c1 * log10(v/v0) + c2 * log10(v/v0)^2 + ...)'', where 'v' is the frequency and 'v0' is the reference frequency.
+If ''LogarithmicSI'' is ''false'', the spectral index is interpreted in a way compatible with wsclean, namely as
+''I = I0 + c0 * (v/v0 - 1) + c1 * (v /v0 - 1)^2 + c2 * (v/v0 -1)^3 + ...''
+This definition is also described in the [[https://wsclean.readthedocs.io/en/latest/component_list.html|WSClean documentation]].
 === Using Rotation Measure ===