Not Homework, just a nerd looking for help

Discussion in 'Miscellaneous' started by ThunderAeroI, Mar 29, 2013.

  1. ThunderAeroI

    ThunderAeroI Rear Admiral Rear Admiral

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    I am working on something not associated with homework and I need some help figuring out how to calculate the points of a graph.

    I'd like to have an exponential curve with 72 datapoints where every 8 points a new sinwave starts. The math is way over my head but I am sure my fellow math nerds know how to solve it quickly.

    The image below provides you a better idea of what I am thinking of. Don't take the image literally for anything. It is just an example.

    [​IMG]
     
  2. B.J.

    B.J. Rear Admiral Rear Admiral

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    Simply put, all you'd need to do is add the two different parts of it together. The first part would be your sine function, and the second part your exponential curve. For the sine curve to repeat every 8 points, all you'd need is x={0,1,2,3....}, y=x*sin(2*pi/8).
     
  3. ThunderAeroI

    ThunderAeroI Rear Admiral Rear Admiral

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    Thank you for your reply; however, I am unable to make your equation result in the desired effect. What it produces is a linear line with no cyclical pattern.
     
  4. Miss Chicken

    Miss Chicken Little three legged cat with attitude Premium Member

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    Howrah, Hobart, Tasmania
    Sorry posted in wrong thread and I am unable to help you :(
     
  5. B.J.

    B.J. Rear Admiral Rear Admiral

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    Whoops! I meant to type y=sin(x*2*pi/8). :alienblush:
     
  6. Yoda

    Yoda Rear Admiral Rear Admiral

    Joined:
    Jul 13, 2000
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    ^I don't think that's quite it either. That's more or less a regular looking sine wave.

    Anyway if I'm understanding the question. I agree about the basic idea, that is exponential (say x^2) plus sine wave (sin (x)). That doesn't lead to much of a nice looking line though. Just messing around with the values on a graph, (x/5)^1.5+sin(2x) looks decent enough to me.

    It shouldn't be hard to get points from there. Sine has a period of 2pi, and since i'm using 2x inside of sin, that means the period is effectively just pi. So to get it to cycle every 8 data points, make x = 0, 1*pi/8, 2*pi/8... anyway solving all those to get the data points is an easy job for a spreadsheet so I come up with:

    Code:
    0	0
    0.3926990817	0.7291175302
    0.7853981634	1.0622557996
    1.1780972451	0.8214779881
    1.5707963268	0.1760859923
    1.9634954085	-0.4610191258
    2.3561944902	-0.676509376
    2.7488935719	-0.2994620043
    3.1415926536	0.4980463969
    3.5342917353	1.3013970052
    3.926990817	1.6960409996
    4.3196898987	1.5101221362
    4.7123889804	0.9149696554
    5.1050880621	0.3245847142
    5.4977871438	0.1529935441
    5.8904862255	0.5716021856
    6.2831853072	1.4086879383
    6.6758843889	2.2499017152
    7.0685834706	2.6809065895
    7.4612825523	2.5300167649
    7.853981634	1.9687012432
    8.2466807157	1.4110776136
    8.6393797974	1.2712704116
    9.0320788791	1.7207696326
    9.4247779608	2.5879249918
    9.8174770425	3.4584504107
    10.2101761242	3.9180642099
    10.6028752059	3.7951293683
    10.9955742876	3.2611582147
    11.3882733693	2.7303070404
    11.780972451	2.6167351264
    12.1736715327	3.0919638054
    12.5663706144	3.984371175
    12.9590696961	4.8796969634
    13.3517687778	5.3636830392
    13.7444678595	5.2647139396
    14.1371669412	4.7543217918
    14.5298660229	4.2466811203
    14.9225651046	4.1559680438
    15.3152641863	4.6537194821
    15.7079632679	5.5683279968
    16.1006623496	6.4855467673
    16.4933614313	6.9911301974
    16.886060513	6.9134745293
    17.2787595947	6.4241228398
    17.6714586764	5.9372599147
    18.0641577581	5.8670715044
    18.4568568398	6.3851035845
    18.8495559215	7.3197572435
    19.2422550032	8.2567937006
    19.6349540849	8.7819749512
    20.0276531666	8.7237044151
    20.4203522483	8.2535319631
    20.81305133	7.7856488204
    21.2057504117	7.7342468472
    21.5984494934	8.2708778224
    21.9911485751	9.2239483526
    22.3838476568	10.1792249093
    22.7765467385	10.7224744918
    23.1692458202	10.6821052918
    23.5619449019	10.2296717345
    23.9546439836	9.7793693959
    24.3473430653	9.7453942958
    24.740042147	10.2993021934
    25.1327412287	11.2695035065
    25.5254403104	12.2417683587
    25.9181393921	12.8018672519
    26.3108384738	12.7782117386
    26.7035375555	12.3423594718
    27.0962366372	11.9085091285
    27.4889357189	11.8908597108
    27.8816348006	12.4609698467
    
    
     
  7. ThunderAeroI

    ThunderAeroI Rear Admiral Rear Admiral

    Joined:
    Feb 28, 2002
    Location:
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    Thats it! I was able to configure the variables a little to work like I wanted.

    I ended with: Y=(X/16)^2+COS(7*X)

    Thank you.