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In mathematics, a variable may be continuous or discrete. If it can take on two particular real values such that it can also take on all real values between them (even values that are arbitrarily close together), the variable is continuous in that interval. If it can take on a value such that there is a non-infinitesimal gap on each side of it containing no values that the variable can take on, then it is discrete around that value.〔K.D. Joshi, ''Foundations of Discrete Mathematics'', 1989, New Age International Limited, (), page 7.〕 In some contexts a variable can be discrete in some ranges of the number line and continuous in others. ==Continuous variables== A continuous variable over a particular range of the real numbers is one whose value in that range must be such that, if the variable can take values ''a'' and ''b'' in that range, then it can also take any value between ''a'' and ''b''. The number of permitted values is uncountable. Methods of calculus are often used in problems in which the variables are continuous, for example in continuous optimization problems. In statistical theory, the probability distributions of continuous variables can be expressed in terms of probability density functions. In continuous-time dynamics, the variable ''time'' is treated as continuous, and the equation describing the evolution of some variable over time is a differential equation. The instantaneous rate of change is a well-defined concept. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Continuous and discrete variables」の詳細全文を読む スポンサード リンク
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