Software representation of the ATLAS solenoid magnetic field

The ATLAS solenoid produces a magnetic field which enables the ATLAS Inner Detector to measure track momentum by track curvature. This solenoidal magnetic field was measured using a rotating-arm mapping machine and, after removing mapping machine effects has been understood to 0.05% level. As tracking algorithms require the field strength at many different points, the representation of this magnetic field in the ATLAS software can have a significant impact on the processing time for these algorithms. This paper reviews the field models and mathematical techniques used to decouple machine effects from real field features and evaluate the peformance of different field representations within the ATLAS software.