In the mathematical field of numerical analysis, monotone cubic interpolation is a variant of cubic interpolation that preserves monotonicity of the data set being interpolated. Monotonicity is preserved by linear interpolation but not guaranteed by cubic interpolation.
Monotone cubic Hermite interpolation
Monotone interpolation can be accomplished using cubic Hermite spline with the tangents m i {\displaystyle m_{i}} modified to ensure the monotonicity of the resulting Hermite spline. An algorithm is also available for monotone quintic Hermite interpolation.
Interpolant selection There are several ways of selecting interpolating tangents for each data point. This section will outline the use of the Fritsch–Carlson method. Note that only one pass of the algorithm is required. Let the data points be ( x k , y k ) {\displaystyle (x_{k},y_{k})} indexed in sorted order for k = 1 , … n {\displaystyle k=1,\,\dots \,n} .
… excerpt ends here. Continue reading the full article.

