#!/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
    @param   tension:float      A [0, 1] value of the interpolation tension
    @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()