pchip — Construct or evaluate shape-preserving piecewise cubic Hermite interpolants.
pchip(x, y) builds shape-preserving cubic Hermite interpolants, and pchip(x, y, xq) evaluates them at query points with MATLAB-compatible interpolation behavior.
Syntax
pp = pchip(X, Y)
Vq = pchip(X, Y, Xq)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
X | Any | Yes | — | Strictly increasing sample locations. |
Y | Any | Yes | — | Sample values. |
Xq | Any | Yes | — | Query points. |
Returns
| Name | Type | Description |
|---|---|---|
pp | Any | Piecewise-polynomial struct representation. |
Vq | NumericArray | PCHIP-evaluated values at query points. |
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:pchip:InvalidArgument | Argument count or interpolation option grammar is invalid. | pchip: invalid argument |
RunMat:pchip:InvalidInput | Sample/query inputs are invalid for PCHIP construction or evaluation. | pchip: invalid input |
RunMat:pchip:Internal | PCHIP coefficient generation or tensor assembly fails internally. | pchip: internal interpolation failure |
How pchip works
- Returns the same pp-structure shape used by
spline. - Uses monotonicity-preserving slopes so monotone data does not overshoot between samples.
- Dense real numeric inputs are supported in the initial implementation.
Example
Shape-preserving interpolation
x = [1 2 3];
y = [1 4 9];
yq = pchip(x, y, [1.5 2.5])Expected output:
yq = [2.21875 6.21875]Using pchip with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how pchip changes the result.
Run a small pchip example, explain the result, then change one input and compare the output.
Related Math functions
Elementwise
abs · angle · complex · conj · double · exp · expm1 · factorial · gamma · hypot · imag · ldivide · log · log10 · log1p · log2 · minus · nextpow2 · plus · pow2 · power · rdivide · real · sign · single · sqrt · times
Trigonometry
acos · acosh · asin · asinh · atan · atan2 · atanh · cos · cosd · cosh · deg2rad · rad2deg · sin · sind · sinh · tan · tand · tanh
Reduction
all · any · cummax · cummin · cumprod · cumsum · cumtrapz · diff · gradient · max · mean · median · min · nnz · prod · std · sum · trapz · var
Structure
Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how pchip is executed, line by line, in Rust.
- View the source for pchip in Rust on GitHub
- Learn how the RunMat runtime works
- Found a bug? Open an issue with a minimal reproduction.
About RunMat
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