Sigmoidal (S-shaped) curves are usually a very good approximation to any system which begins increasing exponentially from its original value, but eventually comes up against an upper limit, which it can approach asymptotically, but never actually attain. A good example of such a system is a simple population growth model, which begins with an exponential growth, but eventually approaches a maximum value, determined by the number of the life forms in question that the environment can support.

Sig"moid (?), Sig*moid"al (?), a. [Gr. ; sigma + form, likeness: cf. F. sigmoide.]

Curved in two directions, like the letter S, or the Greek &sigmat;.

Sigmoid flexure Anat., the last curve of the colon before it terminates in the rectum. See Illust. under Digestive. -- Sigmoid valves. Anat. See Semilunar valves, under Semilunar.


© Webster 1913.

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