Descriptor spectra type

The human retina contains only three types of receptors, which respond mainly to light in the red, green, and blue parts of the spectrum. Suppose that we equip a digital camera with filters that model the response characteristics of the receptors found in the retina. If the processing done by the retina and by the brain were completely understood, we could compute the same color constant descriptors as are computed by the human brain. This method could then be used for object recognition based on color. 

For the example in Fig. 2, the Fourier transformed NMR spectra (variables or descriptors being intensity as a function of frequency) were utilized for the creation of the data matrix D. It should be noted that many different descriptors can be used to create D, with the descriptor selection depending on the analysis method and the information to be extracted. For example, in the spectral resolution methods (Section 6), the desired end result is the determination of the true or pure component spectra and relative concentrations present within the samples or mixtures [Eq. (4)]. For this case, the unmodified real spectra Ij co) are commonly used for the chemometric analysis. In contrast, for the non-supervised and supervised methods described in Sections 3 and 4, the classification of a sample into different categories is the desired outcome. For these types of non-supervised and supervised methods the original NMR spectrum can manipulated or transformed to produce new descriptors including... 

Let us evaluate the different properties and applications of a molecular descriptor while keeping the aforementioned requirements for descriptors in mind. We will focus on a particular descriptor type the radial distribution function (RDF). RDF descriptors grew out of the research area of structure-spectrum correlations but are far more than simple alternative representations of molecules. The flexibility of these functions from a mathematical point of view allows applying them in several other contexts. This chapter will give a theoretical overview of RDF descriptors as well as their application for the characterization of molecules, in particular for similarity and diversity tasks. 

Spectra type descriptors describe the shape of an MS, for example peak distribution or symmetry. The centroid of a mass spectrum is defined as... 

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