This script generates the finite position gradient tensors from the incremental position gradient tensors from step i to k of a simulation.
The script stores finite data in the input Elle file in the six attributes from U_ATTRIB_A to -F.

A - F11
B - F12
C - F21
D - F22
E - dx
F - dy

All incr. pos. grad. tensor files should be stored in the same directory. Their name should start with "IncrPosGradTensorXXX.txt".
XXX indicates the 3 digit (filled with zeros) number of their simulation step.

In case the input Elle file does not contain U_FINITE_STRAIN, which stores the finite passive marker positions: 
This attribute is added and the final positions from the last incremental pos. grad. file are stored in the attribute.

Usage:

FS_postprocess_strainanalysis -i file.elle -u A B C D -n

-> file.elle should be the file that contains flynn and passive marker situation at LAST step (B).

A: The start step to use (does not have to be 1), default: 1
B: The last step to use. 
C: Output finite tensor and dx,dy data in text file? (1 for yes, 0 for no (0 is default)
D: Write an Elle file for every INCREMENTAL step (1 for yes, 0 for no (0 is default))
    --> This option will only plot Elle files directly starting with UNODES block. 
        Those will contain the incremental data from the corresponding step. 
        They can also be transformed in a plotting file using FS_plot_strainanalysis. 
        If flynns and bnodes should be plotted, too, those would have to be added from the actual resulting Elle file from this step.
    --> ATTENTION: Potentially produces a lot of files: 
        By default, they are stored in the present working directory, but you can change the store path in line 71 of .cc file (cf. the comment)

Please make sure that B>=A otherwise computation would not make a lot of sense :-)

Hint: If you want to read all incremental tensor files from another directory, change start of the string in line 73 in .cc file accordingly
