printMatrixHelper = function printMatrixHelper(elements) {
      var big = 0;
      for (var i = 0; i < elements.length; i++) {
        if (i !== 0) {
          big = Math.max(big, Math.abs(elements[i]));
        } else {
          big = Math.abs(elements[i]);
        }
      }

      var digits = (big + "").indexOf(".");
      if (digits === 0) {
        digits = 1;
      } else if (digits === -1) {
        digits = (big + "").length;
      }

      return digits;
    }
Helper function for printMatrix(). Finds the largest scalar
in the matrix, then number of digits left of the decimal.
Call from PMatrix2D and PMatrix3D's print() function.