''' p = evalPoly(a,xData,x).  Evaluates Newton's polynomial p at x. The coefficient  vector 'a' can be computed by the function 'coeffts'.  a = coeffts(xData,yData).  Computes the coefficients of Newton's polynomial.'''  def evalPoly(a,xData,x):  n = len(xData) - 1 # Degree of polynomial  p = a[n]  for k in range(1,n+1):    p = a[n-k] + (x -xData[n-k])*p  return pdef coeffts(xData,yData):  m = len(xData) # Number of data points  a = yData.copy()  for k in range(1,m):    a[k:m] = (a[k:m] - a[k-1])/(xData[k:m] - xData[k-1])  return a