FINTERP: Multidimensional Linear Interpolation with Modern Fortran

Can be used to perform multidimensional (1D-6D) linear interpolation of data on a regular grid. The code is written in modern Fortran (2003/2008) and is object-oriented and thread safe.

There are six classes (linear_interp_1d, linear_interp_2d, linear_interp_3d, linear_interp_4d, linear_interp_5d, and linear_interp_6d). Each has three methods: initialize, evaluate, and destroy.

real(wp) :: x(nx),y(ny),z(nz),q(nq),r(nr),s(ns)
real(wp) :: fcn_1d(nx)
real(wp) :: fcn_2d(nx,ny)
real(wp) :: fcn_3d(nx,ny,nz)
real(wp) :: fcn_4d(nx,ny,nz,nq)
real(wp) :: fcn_5d(nx,ny,nz,nq,nr)
real(wp) :: fcn_6d(nx,ny,nz,nq,nr,ns)
real(wp) :: xval,yval,zval,qval,rval,sval,fval
integer :: iflag

type(linear_interp_1d) :: s1
type(linear_interp_2d) :: s2
type(linear_interp_3d) :: s3
type(linear_interp_4d) :: s4
type(linear_interp_5d) :: s5
type(linear_interp_6d) :: s6

!populate the arrays
!...

!initialize the class:
call s1%initialize(x,fcn_1d,iflag)
call s2%initialize(x,y,fcn_2d,iflag)
call s3%initialize(x,y,z,fcn_3d,iflag)
call s4%initialize(x,y,z,q,fcn_4d,iflag)
call s5%initialize(x,y,z,q,r,fcn_5d,iflag)
call s6%initialize(x,y,z,q,r,s,fcn_6d,iflag)

!interpolate:
call s1%evaluate(xval,fval)
call s2%evaluate(xval,yval,fval)
call s3%evaluate(xval,yval,zval,fval)
call s4%evaluate(xval,yval,zval,qval,fval)
call s5%evaluate(xval,yval,zval,qval,rval,fval)
call s6%evaluate(xval,yval,zval,qval,rval,sval,fval)

!free memory:
call s1%destroy()
call s2%destroy()
call s3%destroy()
call s4%destroy()
call s5%destroy()
call s6%destroy()

The library also includes classes for nearest neighbor interpolation (nearest_interp_1d, nearest_interp_2d, ...). The interfaces are the same as for the linear classes.

A fpm.toml file is provided for compiling finterp with the Fortran Package Manager. For example, to build:

fpm build --profile release

By default, the library is built with double precision (real64) real values. Explicitly specifying the real kind can be done using the following preprocessor flags:

For example, to build a single precision version of the library, use:

fpm build --profile release --flag "-DREAL32"

To run the unit tests:

fpm test

To use finterp within your fpm project, add the following to your fpm.toml file:

[dependencies]
finterp = { git="https://github.com/jacobwilliams/finterp.git" }

or, to use a specific version:

[dependencies]
finterp = { git="https://github.com/jacobwilliams/finterp.git", tag = "1.3.0"  }

To generate the documentation using ford, run: ford ford.md

The latest API documentation can be found here. This was generated from the source code using FORD.

The finterp source code and related files and documentation are distributed under a permissive free software license (BSD-style).

• bspline-fortran, B-spline interpolation.
• PCHIP, Piecewise Cubic Hermite Interpolation.
• Regridpack, Linear or cubic interpolation for 1D-4D grids.