Variations of the correlation coefficient can be calculated for different purposes. The molar attenuation coefficient is usually decadic. The Pearson correlation coefficient must therefore be exactly one. See sample correlation coefficient for additional details. The Gini coefficient is a relative measure. Each elliptic curve coefficient requires logp bits. Inequality is commonly measured by economists using the Gini coefficient. Typical values for the coefficient of rolling resistance are 0.001. Several authors have offered guidelines for the interpretation of a correlation coefficient. The classification depends upon the signature of the eigenvalues of the coefficient matrix . Parentheses may be used to represent a binomial coefficient, and also matrices. The reciprocal of the heat transfer coefficient is thermal insulance. The material medium will have a certain emission coefficient and absorption coefficient. It is measured by the coefficient of relationship. They can be used to solve for the diffusion coefficient, .