sentences:  The iterative solver is required to find a point at the given pseudo-arclength, which requires appending an additional
  constraint (the pseudo-arclength constraint) to the n by n+1 Jacobian.It produces a square Jacobian, and if the stepsize is sufficiently small the modified Jacobian is full rank.Pseudo-arclength continuation was independently developed by Edward Riks and Gerald Wempner for finite element applications in the late 1960s, and published in journals in the early 1970s by H.B.