title: Reversed graph plot
body: <p>I was trying to plot a graph using Python's matplotlib. The data that I wanted to plot is this
  <a href="https://i.stack.imgur.com/8OP6f.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8OP6f.jpg" alt="the data"></a></p>
  
  <p>I'm trying to plot <code>y_i</code> with respect to <code>t</code> (<code>t</code> the x axis and <code>y_i</code> the y axis), but somehow I ended up with this graph,
  <a href="https://i.stack.imgur.com/DnQOA.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DnQOA.jpg" alt="graph image here"></a></p>
  
  <p>You can see that there is something wrong with it, and we all know it (as we go higher along the y axis, the number is getting lower instead of higher). The graph is supposed to have negative slope, how do I fix this? (All kind of help will be appreciated)</p>
  
  <p>Here's my code:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  import pandas as pd
  
  e = 2.71828183
  k = -0.043594
  C = 100
  h = 5
  
  def y(t):
      y = C*(e**(k*t))
      return y
  
  def f(Y):
      f = k*Y
      return f
  
  def y_i(Y, F):
      y_i = Y + h*F
      return y_i
  
  #Y = y(x)    
  #F = f(Y)
  data_luruh = {}
  data_luruh['t'] = [x for x in range(0, 101, 5)]
  data_luruh['y'] = [y(x) for x in range(0, 101, 5)]
  data_luruh['y_i'] = [0 for x in range(0, 101, 5)]
  data_luruh['g'] = [0 for x in range(0, 101, 5)]
  
  data_luruh['y_i'][0] = 'NA'
  data_luruh['g'][0] = 'NA'
  
  a = 1
  while a &lt;= 20:
      data_luruh['y_i'][a] = y_i(y((a-1)*5), f(y((a-1)*5)))
      data_luruh['g'][a] = data_luruh['y'][a] - data_luruh['y_i'][a]
      a += 1
  
  df = pd.DataFrame(data=data_luruh)
  print(df)
  
  t_data = data_luruh['t']
  y_data = data_luruh['y']
  yi_data = data_luruh['y_i']
  
  plt.xlabel('t')
  plt.plot(data_luruh['y_i'], 'go')
  plt.show()
  </code></pre>