====== Appendix 18: Record stiffness matrix ======
The subroutine, called RECORD_AK stores in an ASCII output file called NAME.71 the equation system (stiffness matrix, force and displacement) at a defined iteration. According to an identification number IDENT (in loading file 1st line 25th column), it is possible to write the whole stiffness matrix or in morse storage shape for the large simulations. Initially the storage is previewed for the first iteration and the first step. You can change this in LAMIN2 subroutine before the calling of the RECORD_AK subroutine. \\
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Note: You must use Morse storage to record the stiffness matrix. KNSYM (1st line 15th column in the loading file) must be equal to 3.
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The format for the output file is:
==== 1. Dimension of the equation system ====

^(2I5)^^
|NEQUA|number of degree of freedom|
|MXDOF|size of the stiffness matrix|
==== 2. Stiffness matrix ====

=== 2.1. IDENT = 1256-whole storage case ===

^(NEQUAG10.0) on NEQUA lines ^^ 
|AK(IEQ,:)|values of stiffness matrix for the column IEQ|
=== 2.2. IDENT =1257-morse storage case: ===

^(2I5, G10) on (NEQUA*Number of non zero terms by column) lines ^^
|JA(ILI)|Position in the column|
|ICOL|Number of the column|
|AN(ILI)|Value of the stiffness matrix|
==== 3. Force and displacement ====

^ (I5, 2G10) on NEQUA lines^^
|IDOF|Number of the degree of freedom|
|FORCE|Force|
|DISPL|displacement|