Vibration frequency response function can be calculated, thereby characterizing the system. This technique is used in the field of experimental modal analysis to determine the vibration characteristics of a structure. The simple mass–spring–damper model is the foundation of vibration analysis, but what about more complex systems? The mass–spring–damper model described above is called a single degree of freedom (SDOF) model since the mass is assumed to only move up and down. In more complex systems, the system must be discretized into more masses that move in more than one direction, adding degrees of freedom. The major concepts of multiple degrees of
What a Time to Be Alive debuted at number one on the US "Billboard" 200, with 375,000 album-equivalent units; it sold 334,000 copies in its first week, with the remainder of its unit count representing the album's streaming activity and track sales during the tracking week. It became both Drake and Future's second albums to chart at number one on the "Billboard" 200 in 2015 ("If You're Reading This It's Too Late" and "DS2", respectively). In its second week it sold 65,000 copies. As of January 27, 2016, "What a Time to Be Alive" has sold 519,000 copies in the United States. The album was certified