http://homepages.cae.wisc.edu/~suresh/ME964Website/M964Notes/Notes/introfem.pdf
http://www.cs.rpi.edu/~flaherje/pdf/fea4.pdf
https://en.wikipedia.org/wiki/Invertible_matrix
https://www.purplemath.com/modules/mtrxinvr.htm
http://www.cs.fsu.edu/~mascagni/Forsythe_Leibler_MTAC_1950.pdf
https://pveng.com/home/fea-stress-analysis/fea-methods-blog/
https://pveng.com/home/asme-code-design/
https://pveng.com/home/pipe-stress-analysis/