code: private static int idamax(int n, double[] dx, int ix0, int incx) {
          int ix, imax;
          double dmax;
          if (n < 1) {
              return -1;
          }
          if (n == 1) {
              return 0;
          }
          if (incx == 0) {
              return -1;
          }
          ix = (incx < 0) ? ix0 + ((-n + 1) * incx) : ix0;
          imax = ix;
          dmax = Math.abs(dx[ix]);
          for (int i = 1; i < n; i++) {
              ix += incx;
              double dtemp = Math.abs(dx[ix]);
              if (dtemp > dmax) {
                  dmax = dtemp;
                  imax = ix;
              }
          }
          return imax;
      }
docs: Find the index of element having maximum absolute value.