code: function _getCoefficientsFromMaterials(materials) {
    // Initialize coefficients to use defaults.
    let coefficients = {};
    for (let property in Utils.DEFAULT_ROOM_MATERIALS) {
      if (Utils.DEFAULT_ROOM_MATERIALS.hasOwnProperty(property)) {
        coefficients[property] = Utils.ROOM_MATERIAL_COEFFICIENTS[
          Utils.DEFAULT_ROOM_MATERIALS[property]];
      }
    }
  
    // Sanitize materials.
    if (materials == undefined) {
      materials = {};
      Object.assign(materials, Utils.DEFAULT_ROOM_MATERIALS);
    }
  
    // Assign coefficients using provided materials.
    for (let property in Utils.DEFAULT_ROOM_MATERIALS) {
      if (Utils.DEFAULT_ROOM_MATERIALS.hasOwnProperty(property) &&
          materials.hasOwnProperty(property)) {
        if (materials[property] in Utils.ROOM_MATERIAL_COEFFICIENTS) {
          coefficients[property] =
            Utils.ROOM_MATERIAL_COEFFICIENTS[materials[property]];
        } else {
          Utils.log('Material \"' + materials[property] + '\" on wall \"' +
            property + '\" not found. Using \"' +
            Utils.DEFAULT_ROOM_MATERIALS[property] + '\".');
        }
      } else {
        Utils.log('Wall \"' + property + '\" is not defined. Default used.');
      }
    }
    return coefficients;
  }
docs: Generate absorption coefficients from material names.
  @param {Object} materials
  @return {Object}