#!/usr/bin/env python3
# -*- python -*-
# Test of cubic interpolation.
# Load matplotlib.pyplot,
# it can take some time so
# print information about it.
print('Loading matplotlib.pyplot...')
import matplotlib.pyplot as plot
print('Done loading matplotlib.pyplot')
from math import *
def main():
# Create a page with graphs
fig = plot.figure()
# Add graphs
add_graph(fig, 211, [i / 15 for i in range(16)])
add_graph(fig, 212, [sin(6 * i / 15) for i in range(16)])
# Show graphs
plot.show()
def add_graph(fig, graph_pos, input_values):
'''
Add a graph
@param fig:Figure The page to which to add the graph
@param graph_pos:int Where to place the graph
@param input_values:list<float> The input values for each point
'''
# Interpolate data
output_values = interpolate(input_values)
# Number of input points
n = len(input_values)
# Number of output points
m = len(output_values)
# Create graph
graph = fig.add_subplot(graph_pos)
# Plot interpolated data
graph.plot([i / (m - 1) for i in range(m)], output_values, 'b-')
# Plot input data
graph.plot([i / (n - 1) for i in range(n)], input_values, 'ro')
def interpolate(small, tension = 0):
'''
Interpolate data
@param small:list<float> The input values for each point
@return :list<float> The values for each point in a scaled up version
'''
large = [None] * len(small) ** 2
small_, large_ = len(small) - 1, len(large) - 1
# Basis functions
h00 = lambda t : (1 + 2 * t) * (1 - t) ** 2
h10 = lambda t : t * (1 - t) ** 2
h01 = lambda t : t ** 2 * (3 - 2 * t)
h11 = lambda t : t ** 2 * (t - 1)
def tangent(values, index, last):
'''
Calculate the tangent at a point
@param values:list<float> Mapping from points to values
@param index:int The point
@param last:int The last point
@return :float The tangent at the point `index`
'''
if last == 0: return 0
if index == 0: return values[1] - values[0]
if index == last: return values[last] - values[last - 1]
return (values[index + 1] - values[index - 1]) / 2
# Tension coefficent
c_ = 1 - tension
for i in range(len(large)):
# Scaling
j = i * small_ / large_
# Floor, weight, ceiling
j, w, k = int(j), j % 1, min(int(j) + 1, small_)
# Points
pj, pk = small[j], small[k]
# Tangents
mj, mk = c_ * tangent(small, j, small_), c_ * tangent(small, k, small_)
# Interpolation
large[i] = h00(w) * pj + h10(w) * mj + h01(w) * pk + h11(w) * mk
return large
# Plot interpolation
main()
