.. _auto_curve_check_monotonicity:

*CHECK CURVE Y-MONOTONICITY (MAT_024 VS MAT_187 GATE)*
======================================================

Detect strictly-descending y-axis segments in a curve. For material calibration this is the MAT_024-vs-MAT_187 model-selection gate: a descending sigma_y(eps_p) hardening curve means MAT_024 radial-return is the wrong model (it needs a non-negative tangent modulus); use *MAT_187 (SAMP-1) for softening polymers.

When to use
-----------

Classification: **data**.

Tagged: ``curve``, ``monotonicity``, ``reversal``, ``mat24``, ``mat187``, ``hardening``, ``material_calibration``.

Inputs
------

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 20 20 20

   * - Label
     - ID
     - Type
     - Default
     - Required
     - Description
   * - Curve
     - curve
     - vector
     - —
     - ✓
     - Input curve (X/Y vector pair). For the MAT_024 gate pass the RAW (un-enforced) effective-plastic hardening curve eps_p vs sigma_y.
   * - Tolerance
     - tolerance
     - scalar
     - 0
     - 
     - Reversal threshold: a segment counts as a reversal when y[i] < y[i-1] - tolerance. Default 0 (strict), so flat perfect-plasticity segments are NOT flagged.

Outputs
-------

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 20

   * - Label
     - ID
     - Type
     - Description
   * - curve_check_monotonicity_output_1
     - curve_check_monotonicity_output_1
     - keyvalue
     - Reversal report: n_points, reversal_count, is_monotonic, reversals [{index,y_prev,y}], first_reversal_index, and a message. A reversal means MAT_024 radial-return is invalid (descending sigma_y(eps_p)) -- use *MAT_187 (SAMP-1).

Disciplines
-----------

- engineering.material.calibration
- data.curve.transform

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