double mean(int n, double x[]);             /* Mean                         */
double sdev(int n, double x[]);             /* Standard Deviation           */
double var(int n, double x[]);              /* Variance                     */
double corr(int n, double x[], double y[]); /* Correlation                  */
double cov(int n, double x[], double y[]);  /* Covariance                   */
void linreg(int n, double x[], double y[],  /* Linear Regression y =        */
         double *a, double *b, double *c);  /* a+b*x+c*e where e is N(0,1)  */
double normsim(void);                       /* Very approximately simulated */
                                            /* Random Normal Distribution   */