# Python script to generate the Standard Linear Correlation Coefficient
# slide for the presentation at the CCP4 Study Weekend 2001.
#
# Software required to run this script (this software is freely available):
#     Python 1.5.2, http://www.python.org/
#     ReportLab 1.00, http://www.reportlab.com/
#
# conversion of resulting PDF file to GIF (for import in PowerPoint):
#   Photoshop -> File -> Open *.pdf, Resolution = 150 pixels/inch
#                File -> Save for Web

import math
import random
from reportlab.pdfgen import canvas
from reportlab.lib.units import inch

random.seed(123456)

golden_ratio = (math.sqrt(5.) + 1.) / 2.

def compute_cc(x, y):
  Nxy = len(x)
  assert Nxy == len(y)
  Sx = 0.
  Sx2 = 0.
  Sy = 0.
  Sy2 = 0.
  Sxy = 0.
  for i in xrange(Nxy):
    Sx = Sx + x[i]
    Sx2 = Sx2 + x[i] * x[i]
    Sy = Sy + y[i]
    Sy2 = Sy2 + y[i] * y[i]
    Sxy = Sxy + x[i] * y[i]
  d = (  (Sx2 - Sx * Sx / Nxy)
       * (Sy2 - Sy * Sy / Nxy))
  c = 0.
  if (d > 0.):
    c = (Sxy - Sx * Sy / Nxy) / math.sqrt(d)
  return c

class CCCanvas(canvas.Canvas):

  def __init__(self, filename):
    self.px = (3 * golden_ratio + 0.4) * inch
    self.py = 3.4 * inch
    canvas.Canvas.__init__(self, filename, pagesize = (self.px, self.py))
    self.closing = 0
    self.setup_coordiante_system()

  def setup_coordiante_system(self):
    self.translate(0.48 * inch, 0.3 * inch)
    self.scale(1.1 * inch, 1.1 * inch)

  def showPage(self):
    if (not self.closing):
      canvas.Canvas.showPage(self)
      self.setup_coordiante_system()

  def save(self):
    self.closing = 1
    canvas.Canvas.save(self)

def scatter_plot(c, origin, x, y):
  assert len(x) == len(y)
  c.saveState()
  c.translate(origin[0], origin[1])
  c.setStrokeColorRGB(0, 0, 0)
  c.setLineWidth(0.01)
  c.line(0, 0, 1, 0)
  c.line(0, 0, 0, 1)
  c.setFillColorRGB(0, 0, 0)
  p = c.beginPath()
  p.moveTo(1, 0)
  p.lineTo(0.95, 0.024)
  p.lineTo(0.95, -0.024)
  p.close()
  c.drawPath(p, stroke = 0, fill = 1)
  p = c.beginPath()
  p.moveTo(0, 1)
  p.lineTo(-0.024, 0.95)
  p.lineTo(0.024, 0.95)
  p.close()
  c.drawPath(p, stroke = 0, fill = 1)
  c.setFont("Helvetica", 0.1)
  c.drawCentredString(0.9, -0.1, 'x')
  c.drawCentredString(-0.1, 0.9, 'y')
  cc = compute_cc(x, y)
  caption = 'CC = %5.2f' % (cc,)
  print caption
  c.drawCentredString(0.5, 1.07, caption)
  for i in xrange(len(x)):
    c.circle(x[i], y[i], 0.01, stroke = 0, fill = 1)
  c.restoreState()

if (__name__ == '__main__'):

  origins = (
    (0, 1.45),
    (1.4, 1.45),
    (2.8, 1.45),
    (0, 0),
    (1.4, 0),
    (2.8, 0),
  )

  c = CCCanvas('plot.pdf')

  nPoints = 100

  x = [0] * nPoints
  for i in xrange(nPoints): x[i] = random.random()
  y = [0] * nPoints

  pos = 0
  for f in (0., 0.6, 1.3, -1., 0.9, 4.):
    if (f < 0.):
      for i in xrange(nPoints): y[i] = math.fmod(1. - x[i], 1.)
    else:
      for i in xrange(nPoints):
        while 1:
          y[i] = x[i] + (random.random() - 0.5) * f
          if (y[i] >= 0. and y[i] < 1.): break
    scatter_plot(c, origins[pos], x, y)
    pos = pos + 1

  c.showPage()
  c.save()