inequalities issue: 0<=-0.0 is not true

Question

I have an if statement within a for loop which runs through a number values of x and calculates a value of h based on the x. I have included the code below. At time zero (t=0.0) xa=-0.0 and xb =0.0.

The problem arrises when x=0. At x=0 I want the code to follow the first if statement as x is less than or equal to 0. However it doesnt it goes to the last if statement and carries that out. Now my thinking is that the problem is something to do with x= 0 and xa=-0.0 and python doesn't like this?

If anyone could shed any light on the subject as to why this occurs and if there is a solution to the problem or if indeed there is a different problem, that would be great.

__author__="ahe"
__date__ ="$05-Aug-2014 11:22:44$"

import numpy as np
import matplotlib.pyplot as plt 
import math 
import sys
from math import sqrt  
import decimal
import pylab 

nx, ny = (100,100)
x5 = np.linspace(-2000,2000,nx)
y5 = np.linspace(0,600,ny)
xv,yv = np.meshgrid(x5,y5)
x = np.arange(-2000.0,2001.0,1.0)
print len (x)

h0=0.03
g=9.81
t=0.0

term1=4.0/(9.0*g)
term2=math.sqrt(g*h0)
print 'term1=',term1,'term2=',term2 

xa=-term2*t
xb=term2*2*t

h=np.zeros(len(x))

for i in range (len(x)):
   if x[i]<=xa:
      h[i]=h0
   elif (xa<x[i]<xb):
      h[i]=term1*((term2-(x[i]/(t*2.0)))**2.0)
   else:
      h[i]=0


print 'xa=',xa,'xb=',xb

h1=np.zeros(len(x))

f = open(r'C:\opentelemac\bluetang\examples\telemac2d\ritter\4D0.i3s', 'r')
while True:
   line = f.readline()
   if line[0] not in [':','#']: break
ran = int(line.split()[0])
length = np.zeros(ran)
wse =  np.zeros(ran)
for i in range (ran):
   fields = f.readline().split()
   length[i] = float(fields[0])
   wse[i] = float(fields[2])
   all =[length[i],wse[i]]

print x[1995:2005]
print h[1995:2005]



plt.figure(2)
plt.plot(length,h, marker='o', linestyle='--')
plt.plot(length,wse)
plt.legend(['Analytical solution_0','Model_0'], loc='upper right')
plt.show()

Answer 1

Actually it is true

Python 2.7.4 (default, Sep 26 2013, 03:20:26) 
[GCC 4.7.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 0 <= -0.0
True

So you probably did not diagnose your problem correctly.