function str(a) {
  return 'mat3(' + a[0] + ', ' + a[1] + ', ' + a[2] + ', ' + a[3] + ', ' + a[4] + ', ' + a[5] + ', ' + a[6] + ', ' + a[7] + ', ' + a[8] + ')';
}
Returns a string representation of a mat3

@param {mat3} a matrix to represent as a string
@returns {String} string representation of the matrix