sigmoid

As adjectives the difference between sigmoid and portly

is that sigmoid is (geometry) curved in two directions, like the letter "s", or the greek (sigma) while portly is somewhat fat, pudgy, overweight.

As a noun sigmoid

is (mathematics) a function having a graph whose shape is sigmoid see and mathworld http://mathworldwolframcom/sigmoidfunctionhtml.

As nouns the difference between sigmoid and sigmoidicity

is that sigmoid is a function having a graph whose shape is sigmoid. See Wikipedia and Mathworld while sigmoidicity is the quality of being sigmoid.

As an adjective sigmoid

is curved in two directions, like the letter "S", or the Greek ς (sigma).