Planck's law In 1880, André-Prosper-Paul Crova published a diagram of the three-dimensional appearance of the graph of the strength of thermal radiation as a function of wavelength and temperature. He determined the spectral variable by use of prisms. He analyzed the surface through what he called "isothermal" curves, sections for a single temperature, with a spectral variable on the abscissa and a power variable on the ordinate. He put smooth curves through his experimental data points. They had one peak at a spectral value characteristic for the temperature, and fell either side of it towards the horizontal axis. Such spectral sections are
Spectral abscissa the left half plane, i.e. formula_3 Spectral radius Spectral abscissa In mathematics, the spectral abscissa of a matrix or a bounded linear operator is the supremum among the real part of the elements in its spectrum, sometimes denoted as formula_1 Let λ, ..., λ be the (real or complex) eigenvalues of a matrix "A" ∈ C. Then its spectral abscissa is defined as: For example, if the set of eigenvalues were = {1+3i,2+3i,4-2i}, then the Spectral abscissa in this case would be 4. It is often used as a measure of stability in control theory, where a continuous system is