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POplot a huge amount of data points
 

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  1. POplot a huge amount of data points
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    <p>I have encountered a strange problem: when I store a huge amount of data points from a nonlinear equation to 3 arrays (x, y ,and z) and then tried to plot them in a 2D graph (theta-phi plot, hence its 2D). </p> <p>I tried to eliminate points needed to be plotted by sampling points from every 20 data points, since the z-data is approximately periodic. I picked those points with z value just above zero to make sure I picked one point for every period. </p> <p>The problem arises when I tried to do the above. I got only a very limited number of points on the graph, approximately 152 points, regardless of how I changed my initial number of data points (as long as it surpassed a certain number of course). <img src="https://i.stack.imgur.com/fUdke.png" alt="graph"></p> <p>I suspect that it might be some command I use wrongly or the capacity of array is smaller then I expected (seems unlikely), could anyone help me find out where is the problem?</p> <pre><code>def drawstaticplot(m,n, d_n, n_o): counter=0 for i in range(0,m): n=vector.rungekutta1(n, d_n) d_n=vector.rungekutta2(n, d_n, i) x1 = n[0] y1 = n[1] z1 = n[2] if i%20==0: xarray.append(x1) yarray.append(y1) zarray.append(z1) for j in range(0,(m/20)-20): if (((zarray[j]-n_o)&gt;0) and ((zarray[j+1]-n_o)&lt;0)): counter= counter +1 print zarray[j]-n_o,counter plotthetaphi(xarray[j],yarray[j],zarray[j]) def plotthetaphi(x,y,z): phi= math.acos(z/math.sqrt(x**2+y**2+z**2)) theta = math.acos(x/math.sqrt(x**2 + y**2)) plot(theta, phi,'.',color='red') </code></pre> <p>Besides, I tried to apply the code in the following <a href="https://stackoverflow.com/questions/4082298/scatter-plot-with-a-huge-amount-of-data">SO question</a> to my code, I want a very similar result except that my data points are not randomly generated.</p>
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    1. COHmm. Your indentation looks weird to me -- it should be four spaces everywhere, but look at how far over your `if (((zarray[j]` line is. Run your program with `-tt`, e.g. `python -tt yourprogramname.py` to rule out tab/space errors. I'm also not sure I understand what your `j` loop is doing.
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    2. COi-loop creates 3 arrays, sampling out one point for every 20 points, and putting it into arrays. j-loop considers only those picked out points, hence its size is "m/20". I want pick out a point for every period of z, so I choose those z data that's just above zero in the circumstance that z data is going from positive to negative value.
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    3. COYou are having aliasing issues. Do the loops on the other order and I bet you would get a lot more points. Also look into using the numpy built-ins.
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