Re: Drawing Sinus curve in Python

From	Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject	Re: Drawing Sinus curve in Python
Date	2014-06-01 11:06 -0400
Organization	IISS Elusive Unicorn
References	<c9855239-abca-4753-ad02-2fcf45e56e97@googlegroups.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.10523.1401635208.18130.python-list@python.org> (permalink)

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On Sun, 1 Jun 2014 05:17:07 -0700 (PDT), Farzad Torabi
<seyedfarzad.torabi@gmail.com> declaimed the following:

>Hi Experts
>
> I am trying to draw a sine curve in Python , well first I had a script that i could draw a function curve in this way : 
>
>xMax = 25.0
>points = []
>for i in range(100):
>  x = (float(i)/99)*xMax
>  y = math.sqrt(x)
>  points.append([x,y])
>
>s.Spline(points=points)
>
>
>first i have questions that : what does the line x = (float(i)/99)*xMax do ? why do we multiply it by 
>

	{Presuming Python 2.x} 

	The easiest way to find out what the line is doing is to just add a few
print statements:

>>> import math
>>> xMax = 25.0
>>> point = []
>>> for i in range(100):
... 	x = (i / 99.0) * xMax
... 	y = math.sqrt(x)
... 	print "%5d\t%10.6f\t%10.6f" % (i, x, y)
... 	
    0	  0.000000	  0.000000
    1	  0.252525	  0.502519
    2	  0.505051	  0.710669
    3	  0.757576	  0.870388
    4	  1.010101	  1.005038
    5	  1.262626	  1.123666
    6	  1.515152	  1.230915
    7	  1.767677	  1.329540
    8	  2.020202	  1.421338
    9	  2.272727	  1.507557
   10	  2.525253	  1.589104
   11	  2.777778	  1.666667
   12	  3.030303	  1.740777
   13	  3.282828	  1.811858
   14	  3.535354	  1.880254
   15	  3.787879	  1.946247
   16	  4.040404	  2.010076
   17	  4.292929	  2.071939
   18	  4.545455	  2.132007
   19	  4.797980	  2.190429
   20	  5.050505	  2.247333
   21	  5.303030	  2.302831
   22	  5.555556	  2.357023
   23	  5.808081	  2.409996
   24	  6.060606	  2.461830
   25	  6.313131	  2.512595
   26	  6.565657	  2.562354
   27	  6.818182	  2.611165
   28	  7.070707	  2.659080
   29	  7.323232	  2.706147
   30	  7.575758	  2.752409
   31	  7.828283	  2.797907
   32	  8.080808	  2.842676
   33	  8.333333	  2.886751
   34	  8.585859	  2.930164
   35	  8.838384	  2.972942
   36	  9.090909	  3.015113
   37	  9.343434	  3.056703
   38	  9.595960	  3.097735
   39	  9.848485	  3.138230
   40	 10.101010	  3.178209
   41	 10.353535	  3.217691
   42	 10.606061	  3.256695
   43	 10.858586	  3.295237
   44	 11.111111	  3.333333
   45	 11.363636	  3.370999
   46	 11.616162	  3.408249
   47	 11.868687	  3.445096
   48	 12.121212	  3.481553
   49	 12.373737	  3.517632
   50	 12.626263	  3.553345
   51	 12.878788	  3.588703
   52	 13.131313	  3.623715
   53	 13.383838	  3.658393
   54	 13.636364	  3.692745
   55	 13.888889	  3.726780
   56	 14.141414	  3.760507
   57	 14.393939	  3.793935
   58	 14.646465	  3.827070
   59	 14.898990	  3.859921
   60	 15.151515	  3.892495
   61	 15.404040	  3.924798
   62	 15.656566	  3.956838
   63	 15.909091	  3.988620
   64	 16.161616	  4.020151
   65	 16.414141	  4.051437
   66	 16.666667	  4.082483
   67	 16.919192	  4.113295
   68	 17.171717	  4.143877
   69	 17.424242	  4.174236
   70	 17.676768	  4.204375
   71	 17.929293	  4.234300
   72	 18.181818	  4.264014
   73	 18.434343	  4.293523
   74	 18.686869	  4.322831
   75	 18.939394	  4.351941
   76	 19.191919	  4.380858
   77	 19.444444	  4.409586
   78	 19.696970	  4.438127
   79	 19.949495	  4.466486
   80	 20.202020	  4.494666
   81	 20.454545	  4.522670
   82	 20.707071	  4.550502
   83	 20.959596	  4.578165
   84	 21.212121	  4.605662
   85	 21.464646	  4.632995
   86	 21.717172	  4.660169
   87	 21.969697	  4.687184
   88	 22.222222	  4.714045
   89	 22.474747	  4.740754
   90	 22.727273	  4.767313
   91	 22.979798	  4.793725
   92	 23.232323	  4.819992
   93	 23.484848	  4.846117
   94	 23.737374	  4.872102
   95	 23.989899	  4.897948
   96	 24.242424	  4.923660
   97	 24.494949	  4.949237
   98	 24.747475	  4.974683
   99	 25.000000	  5.000000
>>> 

	It is scaling the range 0..99 into 0.0..25.0. 

	NOTE: I used (i / 99.0) since the compiler, after your float(i), is
going to have to convert the integer 99 into a float before doing the
division -- so I just provided the constant as a float ahead of time, and I
let the compiler convert the integer i to a float on its own.

>and then when I wanted to draw a sine curve I found this one : 
>
>import math
>
>for angle in range(????):
>    y = math.sin(math.radians(angle))
>    print(y)
>
>first , here instead of ???? can we put 2*pi ?

	Did you try?

	Short answer: no... The range() function only works with integers. You
could, however, scale it to a value providing enough steps, and then divide
by the scaling factor to get the actual value.

>>> for i in range(int(2.0 * math.pi * 100.0)):
... 	x = i / 100.0
... 	y = math.sin(x)
... 	print "%5d\t%10.6f\t%10.6f" % (i, x, y)
... 	
    0	  0.000000	  0.000000
    1	  0.010000	  0.010000
    2	  0.020000	  0.019999
    3	  0.030000	  0.029996
    4	  0.040000	  0.039989
    5	  0.050000	  0.049979
    6	  0.060000	  0.059964
    7	  0.070000	  0.069943
    8	  0.080000	  0.079915
    9	  0.090000	  0.089879
   10	  0.100000	  0.099833
   11	  0.110000	  0.109778
   12	  0.120000	  0.119712
   13	  0.130000	  0.129634
   14	  0.140000	  0.139543
   15	  0.150000	  0.149438
   16	  0.160000	  0.159318
   17	  0.170000	  0.169182
   18	  0.180000	  0.179030
   19	  0.190000	  0.188859
   20	  0.200000	  0.198669
   21	  0.210000	  0.208460
   22	  0.220000	  0.218230
   23	  0.230000	  0.227978
   24	  0.240000	  0.237703
   25	  0.250000	  0.247404
 ...
  620	  6.200000	 -0.083089
  621	  6.210000	 -0.073120
  622	  6.220000	 -0.063143
  623	  6.230000	 -0.053160
  624	  6.240000	 -0.043172
  625	  6.250000	 -0.033179
  626	  6.260000	 -0.023183
  627	  6.270000	 -0.013185
>>> 


>
>second i wanted to try this method instead:
>
>xMax = pi
>Lamda = 200
>points = []
>for i in range(Lamda):
>  x = (float(i)/99)*xMax
>  y = math.sin(x)
>  points.append([x,y])
>
>it actually works much better and creates an actual sine curve but the lengths are not really what i want , also if i want to draw a straight line I use this command :
>
>xMax = 1
>Lamda = 200
>points = []
>for i in range(Lamda):
>  x = (float(i)/99)
>  y = xMax
>  points.append([x,y])
>
>but then the problem will be that I can not control the length of this line and the sine curve , that should be equal

	Well, consider -- the longest "x" value in the first is going to be

>>> 199.0 / 99.0 * math.pi
6.314918566306756

but the longest "x" in the second is just

>>> 199.0 / 99.0
2.01010101010101
>>> 

	To plot multiple curves on the same horizontal scale, the formula
controlling the value of "x" has to be the SAME. Moreover, for a straight
line, any decent plotting package should only need the first and last
points of the line, so the whole for-loop can be extracted out:

line = [ [0.0 / 99.0 * math.pi, xMax],
		[199.0 / 99.0 * math.pi, xMax]	]
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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Thread

Drawing Sinus curve in Python Farzad Torabi <seyedfarzad.torabi@gmail.com> - 2014-06-01 05:17 -0700
  Re: Drawing Sinus curve in Python Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-06-01 14:53 +0000
  Re: Drawing Sinus curve in Python Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-06-01 11:06 -0400

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