Fit death probablities or death rates using the 10-parameter model developed by de Beer and Janssen of the Netherlands Interdisciplinary Demographic Institute $$ q_x = \frac{A}{x+B}+a_0\frac{b_0 e^{b_0(x-m_0)}}{1+b_0e^{b_0(x-m_0)}} +[x\le x_0]\frac{b_1 e^{b_1(x-m_1)}}{1+b_1e^{b_1(x-m_1)}} +[x > x_0]\left(\frac{b_2 e^{b_2(x-m_1)}}{1+(b_2/g)e^{b_2(x-m_1)}}+c\right) $$ where \(c\) is determined by continuity at \(x=x_0\). Fitting is done iteratively using a nonlinear optimization routine. The user can set the initial value of any of the parameters using an extrainfo string. For example setting the buildmethod to NIDI:"G=0.6" will set the initial value of \(g\) to 0.6. Because of the large number of parameters it is sometimes desirable to hold one or more of them fixed. This can be done using fit flags in the extrainfo string. For example NIDI:"B0=1","FitB0=0","M0=16","FitM0=0" will fit the model keeping \(b_0\) and \(m_0\) fixed at 1 and 16 respectively.