Spectrum

A spectrum is a usually 2-dimensional plot, of a compound signal, depicting the components by another measure. Sometimes, it is used to refer to the compound signal itself, such as the spectrum of the visible light is all the electromagnetic waves that our eyes can perceive.

There are many specific meanings of spectrum:

In Mathematics

• The frequency spectrum is the result of a frequency transform of a mathematical function into the frequency domain.
• The spectrum of an operator has to do with the invertibility of an operator in function spaces[?].
• The spectrum of a matrix is basically the spectrum of an operator where the matrix is considered as operator. Precisely, it is the set of the matrix's eigenvalues.
• The spectrum of a ring is the set of prime ideals of a ring.
• A (strange) construction, similar to the frequency spectrum, is the cepstrum of the quefrency.

• The electromagnetic spectrum is the power spectrum of an electromagnetic signal - see: electromagnetic spectrum, spectroscopy
• The optical spectrum is the electromagnetic spectrum of visual light
• The power spectrum is the distribution of the energy of a function in the frequency domain, which is actually the same as the magnitude of the frequency spectrum. See spectroscopy.

• The spectrum of activity[?] of an antibiotic evaluates how wide a range of infections can be treated.

• There is a political spectrum which is said to go from left to right.

• There exists the concept of a bipolar spectrum.

• The term spread spectrum is used for certain kinds of signal transmission.

• Spectrum is the name of the defence force of Earth in the science fiction television series Captain Scarlet.