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xi coords of a point in global space

To find out the xi coords of a point in global space

Create an ipdata file containing the point, then do:

fem define data;r;<datafile>
fem define xi;c contain
or
fem define xi;c contain deform

to view

> fem list data
 Total number of data points defined =    2
 Xi positions calculated
     1) nd=    1 NDP=    1 LD=    1 ERR=  0.7016E-01
                 ZD:    0.400E+00  0.200E+00  0.170E+00  0.000E+00
                     (  0.400E+00  0.200E+00  0.170E+00)
                 WD:    0.100E+01  0.100E+01  0.100E+01  0.000E+00
                 XID:   0.772E+00  0.279E+00  0.722E+00
     2) nd=    2 NDP=    2 LD=    4 ERR=  0.6740E-01
                 ZD:    0.600E+00  0.200E+00  0.170E+00  0.000E+00
                     (  0.600E+00  0.200E+00  0.170E+00)
                 WD:    0.100E+01  0.100E+01  0.100E+01  0.000E+00
                 XID:   0.233E+00  0.286E+00  0.551E+00

The global coords are labelled ZD, the corresponding xi coords are labelled XID.

> fem list xi
nd =    1  LD =    1  XID =    0.7721935E+00   0.2791389E+00   0.7216874E+00
nd =    2  LD =    4  XID =    0.2326539E+00   0.2863352E+00   0.5506285E+00
The element number is labelled LD and the xi coords are labelled XID and will match the ouput of fem list data

To find out the strain at a point in global space

Create  the data and xi points as above, list xi to find out the element number and xi coords as above then list strain at the xi points as shown below.
> fem li strain xi_point xi_1 0.2326539E+00 xi_2 0.2863352E+00 xi_3 0.5506285E+00 ele 4

 Class 1 (nx=1) Region 1:

 Element  4 strain solutions:

 pt.  1 X(j,0):  0.6163E+00  0.1432E+00  0.1377E+00  0.0000E+00
 ====== Z(j,0):  0.6000E+00  0.2000E+00  0.1700E+00 -0.5995E+00
         Xi(i):  0.2327E+00  0.2863E+00  0.5506E+00
       Physical Greens strains and extension ratios wrt Fibre coords, and principal invariants:
       EG(1,j): -0.1060E+00                         EXR(1):  0.8877E+00  RI1:  0.3464E+01
          2     -0.9656E-02 -0.1762E+00                 2    0.8048E+00  RI2:  0.3402E+01
          3     -0.3021E-01  0.6337E-01  0.5141E+00     3    0.1424E+01  RI3:  0.1020E+01
> fem li strain xi_point xi_1 0.7721935E+00 xi_2 0.2791389E+00 xi_3 0.7216874E+00 ele 1

 Class 1 (nx=1) Region 1:

 Element  1 strain solutions:

 pt.  1 X(j,0):  0.3861E+00  0.1396E+00  0.1372E+00  0.0000E+00
 ====== Z(j,0):  0.4000E+00  0.2000E+00  0.1700E+00 -0.5888E+00
         Xi(i):  0.7722E+00  0.2791E+00  0.7217E+00
       Physical Greens strains and extension ratios wrt Fibre coords, and principal invariants:
       EG(1,j):  0.8471E-02                         EXR(1):  0.1008E+01  RI1:  0.3539E+01
          2      0.3532E-01 -0.1948E+00                 2    0.7812E+00  RI2:  0.3461E+01
          3      0.2483E+00  0.6821E-01  0.4557E+00     3    0.1383E+01  RI3:  0.1017E+01