Calculates the tanh function (not the hyperbolic tangent, but a function based around it) as defined in Galfit User’s Manual, Appendix A (Peng 2010) :param r_in: Spiral inner radius, in pixels. If this goes extremely negative in fitting, fix to 0.

Corresponds to item R1) in the GALFIT feedme definition.

Parameters¶

r_out: Quantity¶

Spiral outer radius, in pixels. Corresponds to item R2) in the GALFIT feedme definition.

theta_out: Quantity¶

Cumulative rotation to outer radius, in degrees. Corresponds to item R3) in the GALFIT feedme definition.

r: Quantity¶

r coordinate of point(s); distance from the centre of the spiral model, in pixels.

Returns¶

output of tanh function