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Sin wave Maximun/minimum finding?

  1. Oct 29, 2008 #1
    For different values of x in positive increasing order,sin wave would be either
    Max or Min, so I plotted all points.how to find out whether wave is max or min
    at a given particular point from X.
    Last edited: Oct 29, 2008
  2. jcsd
  3. Oct 29, 2008 #2


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    Can you describe the problem a bit better? It sounds like you have a sequence of values and some sort of sine function (Asin(w*t+b) as a function of t, A, b and w unknown) and want to know if you've hit a maximum. If that's what you're looking for, you can't do it
  4. Oct 29, 2008 #3
    Well if you're thinking in terms of calculus, you don't need to graph this.

    A function will have a relative maximum or minimum when its derivative is equal to zero (or at the endpoints of a piece of the function you're observing), and you can determine whether its a maximum or minimum by finding when its second derivative is equal to zero. When the second derivative is positive, the graph is concave up, and vice versa. A local maximum happens when you have the first derivative set to zero and the second derivative is negative. A local minimum happens when the first derivative is set to zero and the second derivative is positive. Beware, though, this is a general rule of thumb; there can be instances where the graph does not change concavity, or when a local minimum or maximum can be at the endpoint of such a piece of a function that you're looking at.
  5. Oct 30, 2008 #4
    for Sin(0) wave is minimum,
    for Sin(90) wave is maximum,
    for Example assume at
    1------->Max at x=1 ,y is max
    2-------->Min at x=2,y is min
    n-1----->max at x=n-1,y is max
    n------->min at x=n ,y is min

    with out knowing y value,just with the help of 1,2,3,4...n how to know at a 3 or 4 or n-1
    Y is max or min.

    I got this clues,finding the 'area' bounded by the curve and with provided 1,2,3
    finding out y is max or min at asked point.

    please help me:uhh:,
    Last edited: Oct 30, 2008
  6. Oct 30, 2008 #5

    More clearly it would be like this

    for example
    at x=1 sine wave is Maximum
    at x=2 sine wave is Maximum
    at x=3 sine wave is Min
    at x=4 sine wave is Min
    at x=5 sine wave is Maximum
    at x=6 sine wave is Min
    at x=7 sine wave is Maximum
    at x=8 sine wave is Min
    at x=9 sine wave is Min
    at x=10 sine wave is Min
    at x=n-1 sine wave is Min
    at x=n sine wave is Max.

    I mapped all the points,
    so for x=1,how to find out wave is Max or Min
    with out knowledge of wave.

    I'm thinking like this finding out area bounded
    by curve,and x values are given,so with the help
    of 'area' and x values,I think I can find out y values(Max or Min)

  7. Oct 30, 2008 #6


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    If sin(1) and sin(2) are maxima, then sin(n) is a maximum for all n, as 1 is necessarily a period. I'm not sure what you're trying to get at
  8. Oct 30, 2008 #7
    not like that you are taking sin(1),sin(2)...sin(n) as max

    Just imagine x values in I quadrant in the graph.
    now y values i.e sin wave values are mapped as min or max.

    now have to find out at x=3 wave is max or min with out reading the wave.
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