In fitteia consider the following definitions in the appropriate fields in the fitter module:

1. Independent variable: tau

2. Dependent variable: Mz

3. Expression: Mz=Minf\+(M0-Minf)*p11*exp(-tau/T11)\+(M0-Minf)*(1-p11)*exp(-tau/T12))

4. fitting parameters: Minf,M0,p11,T11,T12

The "\+" will produce a plot where "Mz" and the contributions "Minf", "(M0-Minf)*p11*exp(-tau/T11)", and "(M0-Minf)*(1-p11)*exp(-tau/T12))" will drawn.

In other fitting software substitute "\+" by "+".