/* -------------------------------------------------------------------------  * This program reads bivariate data from a text file and computes the mean,  * standard deviation, minimum, maximum, correlation coefficient and   * regression line angle (theta).  *   * NOTE: the text data file is assumed to be in a two-values-per-line format * (i.e. bivariate format) with NO blank lines in the file.  * * NOTE: for more information relative to the use of this program, see the * header of the analogous univariate program uvs.c  * * Name              : bvs.c (BiVariate Statistics)  * Authors           : Steve Park & Dave Geyer  * Language          : ANSI C   * Latest Revision   : 5-2-99 * Compile with      : gcc -lm bvs.c * Execute with      : a.out < bvs.dat * -------------------------------------------------------------------------  */#include <stdio.h>#include <math.h>typedef struct {   double u;  double v; } bivariate;  int main(void){  long      index;  bivariate data;  bivariate sum = {0.0, 0.0};  bivariate mean;  bivariate stdev;  bivariate min;  bivariate max;  bivariate diff;  double    cosum = 0.0;  double    covariance;  double    correlation;  double    temp;  double    theta;  double    pi = 4.0 * atan(1.0);        /* 3.14159 ... */  scanf("%lf %lf\n", &data.u, &data.v);  if (!feof(stdin)) {    index = 1;    mean  = data;    min   = data;    max   = data;  }  else    index = 0;  while (!feof(stdin)) {    scanf("%lf %lf\n", &data.u, &data.v);    index++;    temp    = (index - 1.0) / index;    diff.u  = data.u - mean.u;    diff.v  = data.v - mean.v;    sum.u  += diff.u * diff.u * temp;    sum.v  += diff.v * diff.v * temp;    cosum  += diff.u * diff.v * temp;    mean.u += diff.u / index;    mean.v += diff.v / index;    if (data.u > max.u)      max.u = data.u;    else if (data.u < min.u)      min.u = data.u;    if (data.v > max.v)      max.v = data.v;    else if (data.v < min.v)      min.v = data.v;  }  if (index > 0) {    stdev.u    = sqrt(sum.u / index);    stdev.v    = sqrt(sum.v / index);    covariance = cosum / index;    if (stdev.u * stdev.v > 0.0)      correlation = covariance / (stdev.u * stdev.v);    else      correlation = 0.0;    sum.u = stdev.u * stdev.u - stdev.v * stdev.v;    sum.v = 2.0 * covariance;    theta = 0.5 * atan2(sum.v, sum.u);    printf("\nfor a bivariate sample of size %ld\n\n", index);    printf("mean.u ...... = %7.3f\n", mean.u);    printf("stdev.u ..... = %7.3f\n", stdev.u);    printf("min.u ....... = %7.3f\n", min.u);    printf("max.u ....... = %7.3f\n\n", max.u);    printf("mean.v ...... = %7.3f\n", mean.v);    printf("stdev.v ..... = %7.3f\n", stdev.v);    printf("min.v ....... = %7.3f\n", min.v);    printf("max.v ....... = %7.3f\n\n", max.v);    printf("correlation ...... = %7.3f\n", correlation);    printf("theta (radians) .. = %7.3f\n", theta);    printf("theta (degrees) .. = %7.3f\n", 180.0 * theta / pi);  }  return(0);}