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    <p>Shiuan, </p> <p>I am still investigating your problem, how ever a few notes:</p> <p>Instead of looping and appending to an array you could do:</p> <h1>select every nth element:</h1> <pre><code># inside IPython console: [2]: a=np.arange(0,10) In [3]: a[::2] # here we select every 2nd element. Out[3]: array([0, 2, 4, 6, 8]) </code></pre> <p>so instead of calcultating runga-kutta on all elements of m:</p> <pre><code>new_m = m[::20] # select every element of m. </code></pre> <p>now call your function like this:</p> <pre><code>def drawstaticplot(new_m,n, d_n, n_o): n=vector.rungekutta1(n, d_n) d_n=vector.rungekutta2(n, d_n, i) x1 = n[0] y1 = n[1] z1 = n[2] xarray.append(x1) yarray.append(y1) zarray.append(z1) ... </code></pre> <h1>about appending, and iterating over large data sets:</h1> <p><code>append</code> in general is slow, because it copies the whole array and then stacks the new element. Instead, you already know the size of n, so you could do:</p> <pre><code>def drawstaticplot(new_m,n, d_n, n_o): # create the storage based on n, # notice i assumed that rungekutta, returns n the size of new_m, # but you can change it. x,y,z = np.zeros(n.shape[0]),np.zeros(n.shape[0]), np.zeros(n.shape[0]) for idx, itme in enumerate(new_m): # notice the function enumerate, make it your friend! n=vector.rungekutta1(n, d_n) d_n=vector.rungekutta2(n, d_n, ite,) x1 = n[0] y1 = n[1] z1 = n[2] #if i%20==0: # we don't need to check for the 20th element, m is already filtered... xarray[idx] = n[0] yarray[idx] = n[1] zarray[idx] = n[2] # is the second loop necessary? if (((zarray[idx]-n_o)&gt;0) and ((zarray[j+1]-n_o)&lt;0)): print zarray[idx]-n_o,counter plotthetaphi(xarray[idx],yarray[idx],zarray[idx]) </code></pre>
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    1. POplot a huge amount of data points
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    1. COI'm not sure whether this helps, but I'll put my runnable full code here.:p [link](http://ideone.com/8Uccg) The idea is to draw a small spinning top animation and try to analyze its movement. Thanks for providing that useful trick of selecting Nth number, but all my n's and d_n's stands for the spinning top's position and velocity vector. At each step, its generated by the last ones, so I'm afraid I still have to calculate the full series.
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    2. CO@Yi-ShiuanHuang, sure it helps, it spares a lot of guessing.
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    3. COThanks for your help, I'm still new to programming. I must have already made a lot of noob mistakes.:p And some of the codes borrowed from other places, hence it's kind of messy to some extent.
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