IVIMFunction gives the IVIM function with 2 comps. IVIMFunction[components] gives the IVIM function. IVIMFunction[components, type] gives the IVIM function. type can be "Normal" or "Exp". componenets can be 2 or 3. output is the function with b, S0, f1, f2, D, pD1, pD2 as parameters. The fraction is defined between 0 and 1, the D, Dp, Dp1 and Dp2 is in mm^2/s.