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--- playground:tempjim [2014/08/28 19:35] – jim_brouzoulis
+++ playground:tempjim [2014/08/28 21:53] (current) – jim_brouzoulis
@@ Line 2: / Line 2: @@
    \renewcommand{\b}[1]{\mathbf{#1}}
 \)
-$$\b{a}$$
+$$\b{a}_{\rm{i}} \rm{b} b$$
 ====== Implementation of a linear plane stress triangle ======
@@ Line 10: / Line 10: @@
 with the internal and external force vectors respectively
-$$\mathbf{f}_{\mathrm{int}} = \int_V \mathbf{B}^{\mathrm{T}} \mathbf{\sigma} \ \mathrm{d}V $$
+$$\b{f}_{\rm{int}} = \int_V \b{B}^{\rm{T}} \b{\sigma} \ \rm{d}V $$
-$$\mathbf{f}_{\mathrm{ext}} = \int_V \mathbf{N}^{\mathrm{T}} \mathbf{b} \ \mathrm{d}V
+$$\b{f}_{\rm{ext}} = \int_V \b{N}^{\rm{T}} \b{b} \ \rm{d}V
-+ \int_{\Gamma} \mathbf{N}^{\mathrm{T}} \mathbf{t} \ \mathrm{d}\Gamma $$
++ \int_{\Gamma} \b{N}^{\rm{T}} \b{t} \ \rm{d}\Gamma $$
 The default solution procedure for solving the equations are a Newton-Rapshon scheme and for this the tangent stiffness matrix is needed,
@@ Line 148: / Line 148: @@
 <file - BasicElement.h>
 </file>
+===== Problem representation - Engineering model =====
+The concept "engineering model" is an abstraction for the problem under
+consideration. It represents the type of analysis to be performed (e.g. static structural, transient heat flow, etc.).
+The base class ''EngngModel'' declares and implements the basic services for assembling
+characteristic components and services for starting the solution step and
+its termination. Derived classes ``know'' the form of governing
+equation and the physical meaning of  particular components.
+They are responsible for forming the governing equation for each solution
+step,  usually by summing contributions from particular elements and
+nodes.ecific load type dependent
+services and implement all necessary services.