NONLIN: A New Version for Simplified Use in BASIC Computer Systems . Published in Methods of Information in Medicine
It allows us to explore "what-if" scenarios that were previously impossible to visualize. The Challenges Ahead
✅ – For well-behaved PK models, it converges reliably with good initial estimates. ✅ Transparent algorithm – Uses Gauss-Newton with Levenberg-Marquardt damping; users understand what's happening. ✅ Lightweight – Runs on very modest hardware (originally DOS, later Windows command line). ✅ No black-box overfitting – Encourages careful model building. nonlin software
Use R (nls, nlme, bbmle) or Python (lmfit, scipy.optimize.curve_fit) for free, flexible nonlinear regression. For PK/PD specifically, Phoenix WinNonlin (commercial) or Monolix (NLME) are far superior. NONLIN is a museum piece – historically important, but painfully outdated.
This process requires immense computational power. A linear analysis of a skyscraper might take minutes; a non-linear analysis of the same building simulating an earthquake could take days. NONLIN: A New Version for Simplified Use in
: The software, along with its companion tool EQ-Tools , has been included in educational materials for the Federal Emergency Management Agency (FEMA) to help teach seismic design. What the Software Does NONLIN: Software for Earthquake Engineering Education
COMSOL takes a different approach—equation-based modeling. While it is a general-purpose solver, its nonlinear capabilities are exceptional for coupled physics (e.g., magnetostriction or thermal expansion of a brake disc). Best for: Academia and multiphysics nonlinear problems. Use R (nls, nlme, bbmle) or Python (lmfit, scipy
: Current source code and historic manuals are archived at the University of Edinburgh's AIAI AIAI, University of Edinburgh 4. General Nonlinear Programming (Software Reviews)
Widely considered the gold standard for nonlinear FEA. Abaqus excels in advanced material modeling (e.g., human tissue, rubber, concrete damage). Its solver is legendary for handling severe contact and large deformation problems that cause other solvers to crash. Best for: Research, advanced manufacturing, biomechanics.
This is the "on/off" problem. When two parts touch, forces transfer instantly. When they separate, the forces vanish. Nonlin software uses iterative solvers (like Newton-Raphson) to find exactly when and where contact happens.
If your engineering team is currently facing failures in physical prototypes that your linear software didn't predict, it is time to invest in a trial license of a dedicated nonlin software package like Abaqus or LS-DYNA. Start with a simple rubber compression test or a snap-fit hook simulation. Once you see the difference between linear and nonlinear results, you will never go back.