如何将浮点数组平滑插入到更大的数组中？

Question

I'm stuck with interpolation in Swift. Can anyone help me with that?

I want to interpolate the float array (say [0, 0, 100, 25, 0, 0, 0, 25, 0, 0, 0] ) into another array with some given size (for example 128 ). I found an article ( Use Linear Interpolation to Construct New Data Points ) that shows, how to achieve this stuff.

There are two ways (you can see the results below, how they perform):

• Linear Interpolation using vDSP_vgenp and
• Smoother (but not for my purposes) Interpolation using vDSP_vlint

The problem is both techniques don't realize my expectations, which illustrated in Screenshot 3 . How can I make my interpolated distribution smoother? I want to see a cube-like curve .

Initial Plot:

Linear Interpolation:

import Accelerate

let n = vDSP_Length(128)
let stride = vDSP_Stride(1)

let values: [Float] = [0, 0, 100, 25, 0, 0, 0, 25, 0, 0, 0]
let indices: [Float] = [0, 11, 23, 34, 46, 58, 69, 81, 93, 104, 116]

var result = [Float](repeating: 0, count: Int(n))

vDSP_vgenp(values, stride, indices, stride, &result, stride, n, vDSP_Length(values.count))

Smooth Interpolation:

import Accelerate
import AVFoundation

let n = vDSP_Length(1024)
let stride = vDSP_Stride(1)

let values: [Float] = [0, 0, 100, 25, 0, 0, 0, 25, 0, 0, 0]
let denominator = Float(n) / Float(values.count - 1)

let control: [Float] = (0 ... n).map {
    let x = Float($0) / denominator
    return floor(x) + simd_smoothstep(0, 1, simd_fract(x))
}

var result = [Float](repeating: 0, count: Int(n))

vDSP_vlint(values, control, stride, &result, stride, n, vDSP_Length(values.count))

Answer 1

It seems to me that the vDSP_vqint quadratic interpolation functions would solve the problem. See the discussion at https://developer.apple.com/documentation/accelerate/1449942-vdsp_vqint .