fix doc

docs/src/details.md

@@ -33,7 +33,7 @@ logREML(\theta,\beta) = -\frac{N-p}{2} - \frac{1}{2}\sum_{i=1}^nlog|V_{\theta, i
 -\frac{1}{2}log|\sum_{i=1}^nX_i'V_{\theta, i}^{-1}X_i|-\frac{1}{2}\sum_{i=1}^n(y_i - X_{i}\beta)'V_{\theta, i}^{-1}(y_i - X_{i}\beta)
 ```
 
-Actually ``\mathcal{L}(\theta) = -2logREML`` used for optimization,  ``-2logREML = L_1(\theta) + L_2(\theta) + \L_3(\theta) + c``, where:
+Actually ``\mathcal{L}(\theta) = -2logREML = L_1(\theta) + L_2(\theta) + \L_3(\theta) + c`` used for optimization, where:
 
 ```math
 L_1(\theta) = \frac{1}{2}\sum_{i=1}^nlog|V_{i}| \\
@@ -43,14 +43,26 @@ L_2(\theta) = \frac{1}{2}log|\sum_{i=1}^nX_i'V_i^{-1}X_i| \\
 L_3(\theta) = \frac{1}{2}\sum_{i=1}^n(y_i - X_{i}\beta)'V_i^{-1}(y_i - X_{i}\beta)
 ```
 
- ```math
-  \nabla\mathcal{L}(\theta) = \nabla L_1(\theta) + \nabla L_2(\theta) + \nabla L_3(\theta)
- ```
+```math
+\nabla\mathcal{L}(\theta) = \nabla L_1(\theta) + \nabla L_2(\theta) + \nabla L_3(\theta)
+```
 
 ```math
 \mathcal{H}\mathcal{L}(\theta) =  \mathcal{H}L_1(\theta)  + \mathcal{H}L_2(\theta) +  \mathcal{H} L_3(\theta)
 ```
 
+##### Initial step
+
+Initial (first) step before optimization may be done:
+
+```math
+\theta_{n+1} = \theta_{n} - \nabla\mathcal{L}(\theta_{n}) * \mathcal{H}^{'}(\theta_{n}) , where \\
+
+\mathcal{H}^{'}(\theta_{n}) = - \mathcal{H}L_1(\theta_{n})  + \mathcal{H} L_3(\theta) , if score \\
+
+\mathcal{H}^{'}(\theta_{n}) =  \mathcal{H} L_3(\theta_{n}) , if ai
+
+```
 
 
 #### Beta (β)