Maths & numbers

Natural cubic spline workspace

Interpolate an ordered point set with natural endpoint conditions and export samples.

Natural cubic spline workspace
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Your inputs

Exact X,Y headings. Plain finite coordinates within ±1 billion.

Up to 25 MB per file, 50,000 data rows, 200 columns and 2 million data cells. Fully blank rows and columns are ignored before row, column and cell limits are checked. Individual tools may have smaller result or chart limits.

Results update as you type. Larger files run when you press Update result.

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A clear answer. Here’s how.

Sorts 2–500 points by X, requiring separations greater than 10⁻¹⁰. Solves the natural cubic spline tridiagonal system with zero second derivatives at both endpoints. The spline passes through supplied points; it is not a smoothing fit and does not extrapolate. First output row is the query, followed by 101 evenly spaced curve samples.

See a worked example

Worked example

A fixed demonstration, separate from the values you enter above.

CSV: X,Y
X,Y
0,1
1,2
2,5
3,10
Query X inside the data range
1.5

Example result

First 5 rows of the example result
XInterpolated Y
1.53.2
01
0.031.0180108
0.061.0360864
0.091.0542916

First row is your query; remaining rows sample the supplied X range. Natural cubic spline: second derivatives are zero at both endpoints; no extrapolation.

Keep going.

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