Thread: Help Wanted: Computing the period of sine-wave input data

  1. #1
    Registered User
    Join Date
    Mar 2012

    Help Wanted: Computing the period of sine-wave input data

    I'm in an intro C programming class, and I need to write a program that uses the output of a previous program I wrote as input to compute the period of a sine wave. We have an interface that reads the input for us, but here is the code I have written so far:

    //estimates the period of given sine data
    #include <stdio.h>
    #include <math.h>
    int main(void)
    //defining variables
    int s;
    double y1=0,y2=0,d,t1=0, t2=0;
           while(1) // until end-of-file or error
        s = scanf("%lf",&d); // try to read one double
    t2=t1, t1++;
     if( s != 1) // could not read one double, must be end-of-file or error
    if ((y1>0&&y2<=0)||(y1<=0&&y2>0)) //if the two data values have opp. signs
      return 0;
    Now it's not like I expected this to print me the period, because I obviously haven't written any code to do anything of the sort. That being said, this prints me all of the values where zero-crossings occur. How can I change the program/write something that will take two of these consecutive values, and subtract one from the other?

    Right now my output is something like:


    And I need to compute, for example, 2*(22.50-9.50)

  2. #2
    Registered User javaeyes's Avatar
    Join Date
    Feb 2012
    If I understand correctly, the data are of the form y = k sin (x) + h , not y = sin x. This won't affect the period though. Also the data are not very granular. Here is one crude alg to figure out the period. Check for one y max , and store the x1 value. check for the next y max and store the x2 value. Your period will be x2 - x1. There is probably some other more elegant solution, which someone will post when daybreak comes.

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