// The Wikipedia example
// http://en.wikipedia.org/wiki/Simple_linear_regression
//
float x[] = {33, 83, 130.33, 181, 231.33, 278.33};
float y[] = {50, 100, 150, 200, 250, 300};
int xNum = sizeof(x) / sizeof(float);
int yNum = sizeof(y) / sizeof(float);
float lrCoef[2] = {0, 0};

// initialize variables
float sum_x = 0;
float sum_y = 0;
float sum_xy = 0;
float sum_xx = 0;

void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT);
  pinMode(3, INPUT);
  delay(200);
  // call simple linear regression algorithm
  simpLinReg(x, y, lrCoef, xNum);
  Serial.println("Wikipedia example should give: beta= 61.272, alpha= -39.062");
  Serial.println();
  Serial.println("Calculated coefficients:");
  Serial.println(" BETA ALPHA");
  Serial.print("f(x)= ");
  //Serial.print("BETA: ");
  Serial.print(lrCoef[0], 4);

  //Serial.print(", ALPHA");
  if (lrCoef[1] > 0) {
    Serial.print("*x + ");
  }
  else {
    Serial.print("*x ");
  }
  Serial.println(lrCoef[1], 4);
}
int alr = 0;
int lsAlr = 0;
int step = 0;
bool readComplete = false;
// void loop() {
//   // if(!digitalRead(2)){
//   //   readComplete = false
//   //   step ++;
//   // }
//   if (step == 0 && !readComplete) {
//     alr = analogRead(A0);
//     if (abs(alr - lsAlr) / alr < 0.02) {
//       x[]
//       step ++;
//     }
//   }

//   // Serial.println("2");
//   if (!digitalRead(3))Serial.println("3");
// }


void simpLinReg(float* x, float* y, float* lrCoef, int n) {
  // pass x and y arrays (pointers), lrCoef pointer, and n. The lrCoef array is comprised of the slope=lrCoef[0] and intercept=lrCoef[1]. n is length of the x and y arrays.
  // http://en.wikipedia.org/wiki/Simple_linear_regression

  // calculations required for linear regression
  for (int i = 0; i < n; i++) {
    sum_x = sum_x + x[i];
    sum_y = sum_y + y[i];
    sum_xy = sum_xy + x[i] * y[i];
    sum_xx = sum_xx + x[i] * x[i];
  }
  // simple linear regression algorithm
  lrCoef[0] = (n * sum_xy - sum_x * sum_y) / (n * sum_xx - sum_x * sum_x);
  lrCoef[1] = (sum_y / n) - ((lrCoef[0] * sum_x) / n);
}