''' p = rational(xData,yData,x)  Evaluates the diagonal rational function interpolant p(x)  that passes through he data points'''  from numpy import zerosdef rational(xData,yData,x):  m = len(xData)  r = yData.copy()  rOld = zeros(m)  for k in range(m-1):    for i in range(m-k-1):      if abs(x - xData[i+k+1]) < 1.0e-9:        return yData[i+k+1]      else:        c1 = r[i+1] - r[i]        c2 = r[i+1] - rOld[i+1]        c3 = (x - xData[i])/(x - xData[i+k+1])        r[i] = r[i+1] + c1/(c3*(1.0 - c1/c2) - 1.0)        rOld[i+1] = r[i+1]  return r[0]