Use consistent nonlinear algorithm

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.91837% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 90.8012%. Comparing base (024fd40) to head (9985d09).

Files	Patch %	Lines
Material/Material2D/DuncanSelig.cpp	95.9184%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #197 +/- ## ================================================ + Coverage 90.7600% 90.8012% +0.0413% ================================================ Files 662 662 Lines 29253 29232 -21 Branches 3330 3327 -3 ================================================ - Hits 26550 26543 -7 + Misses 2703 2689 -14 ```

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